An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications
An accumulation mode SOI pMOSFET model for simulation of analog circuits meant for high-temperature applications is presented in the paper. The model is based on explicit expressions for the drain current with an infinite order of continuity what assures smooth transitions between different operatio...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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| Cite this: | An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications / Yu. Houk, B. Iniguez, D. Flandre, A. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 43-54. — Бібліогр.: 15 назв. — англ. |
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Houk, Yu. Iniguez, B. Flandre, D. Nazarov, A. 2017-06-14T17:29:50Z 2017-06-14T17:29:50Z 2006 An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications / Yu. Houk, B. Iniguez, D. Flandre, A. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 43-54. — Бібліогр.: 15 назв. — англ. 1560-8034 PACS 85.30.Tv, 85.30.De https://nasplib.isofts.kiev.ua/handle/123456789/121592 An accumulation mode SOI pMOSFET model for simulation of analog circuits meant for high-temperature applications is presented in the paper. The model is based on explicit expressions for the drain current with an infinite order of continuity what assures smooth transitions between different operation regimes of the transistor. This model is valid for all regimes of normal operation, demonstrates proper description of high-temperature behavior of the subthreshold and off-state current. The model characteristics show a good agreement with the experimental data for temperatures up to 300 °C. The work was performed in the frame of SPRING project (project #IST-1999-12342), and also was partially supported by NATO CLG (PST CLG 979999). The authors are thankful to T.E. Rudenko, V. Kilchytska and A. Tuor for helpful discussions. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications Article published earlier |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications Houk, Yu. Iniguez, B. Flandre, D. Nazarov, A. |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications |
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analytical accumulation mode soi pmosfet model for high-temperature analog applications |
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Houk, Yu. Iniguez, B. Flandre, D. Nazarov, A. |
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Houk, Yu. Iniguez, B. Flandre, D. Nazarov, A. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Article |
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An accumulation mode SOI pMOSFET model for simulation of analog circuits meant for high-temperature applications is presented in the paper. The model is based on explicit expressions for the drain current with an infinite order of continuity what assures smooth transitions between different operation regimes of the transistor. This model is valid for all regimes of normal operation, demonstrates proper description of high-temperature behavior of the subthreshold and off-state current. The model characteristics show a good agreement with the experimental data for temperatures up to 300 °C.
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1560-8034 |
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https://nasplib.isofts.kiev.ua/handle/123456789/121592 |
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An analytical accumulation mode SOI pMOSFET model for high-temperature analog applications / Yu. Houk, B. Iniguez, D. Flandre, A. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 1. — С. 43-54. — Бібліогр.: 15 назв. — англ. |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
43
PACS 85.30.Tv, 85.30.De
An analytical accumulation mode SOI pMOSFET model
for high-temperature analog applications
Yuri Houk1*, Benjamin Iñiguez2, Denis Flandre3, Alexei Nazarov1
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, 03028 Kyiv, Ukraine
2Universitat Rovira i Virgili (URV), Av. Països Catalans
26, Campus Sescelades, 43007 Tarragona (Catalonia), Spain
3Université Catholique de Louvain (UCL), Bâtiment Maxwell, Place du Levant
3, B-1348 Louvain-la-Neuve, Belgium
*Corresponding author: phone/fax +380445256177, e-mail: houk@lab15.kiev.ua
Abstract. An accumulation mode SOI pMOSFET model for simulation of analog
circuits meant for high-temperature applications is presented in the paper. The model is
based on explicit expressions for the drain current with an infinite order of continuity
what assures smooth transitions between different operation regimes of the transistor.
This model is valid for all regimes of normal operation, demonstrates proper description
of high-temperature behavior of the subthreshold and off-state current. The model
characteristics show a good agreement with the experimental data for temperatures up to
300 °C.
Keywords: high-temperature electronics, AM SOI pMOSFET, ∞C -continuous model.
Manuscript received 10.10.05; accepted for publication 15.12.05.
1. Introduction
Nowadays high-temperature electronics is a very
important technology, especially for oil & gas, aerospace
and automotive industries. Micronic silicon-on-insulator
(SOI) CMOS technologies have proved to be the most
mature for the 200-350 °C range of operation [1]. In
particular, accumulation-mode (AM) SOI pMOSFETs
appear very promising for the design of analog circuits
operating in the wide temperature range (up to 350 °C)[1].
For developing these circuits, it is necessary to have an
AM SOI pMOSFET model that is continuous in all
regimes of operation, and derivatives of which are also
continuous ( ∞C -continuous model). Such model has not
been developed yet for high temperatures. In this paper,
we present an extension to high temperatures of the room-
temperature models developed by B. Iñiguez et al. [2, 3].
2. Model
As it is well known, the AM SOI MOSFETs feature
three possible conduction modes: conduction through
front and back accumulation layers (accumulation
channels) and that through the non-depleted portion of
the Si film, i.e., the quasi-neutral region (body channel)
[4, 5]. The AM SOI pMOSFET model [2] accounts only
two of these conduction modes, which are important
under typical circuit operation (see Fig. 1b): body
current and accumulation current, which appears when a
portion of the front surface is in accumulation. I.e., the
model is valid under the conditions, first, that the back
surface of the Si film is always depleted, there are no
mobile charge at the back interface and therefore current
does not flow at the back interface; and second, the body
current always appears in a central quasi-neutral region
of the film before front accumulation develops (i.e.,
when the gate voltage is swept to negative values in a
pMOSFET).
However, there also exists a special case of full
depletion of the AM SOI pMOSFET film by back-gate
bias and positive charge in the buried oxide (BOX),
which appears if the doping of Si film is low. This
special case can be handled using the equations similar
to the fully depleted (FD) SOI nMOSFET model [3].
This is justified because in both cases the Si film is
fully-depleted, and the conduction takes place in the
(accumulation or inversion) channel at the front Si/SiO2
interface [6].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
44
Fig. 1. Cross section of an AM SOI pMOSFET (a) and conduction in an AM SOI pMOSFET with the front surface partially
depleted, partially accumulated (b).
Therefore, for the first time we develop a high-
temperature model for AM SOI pMOSFETs based on
the room-temperature models for AM SOI pMOSFETs
[2] and FD enhancement mode (EM) nMOSFETs [3].
2.1. Overview of room-temperature AM SOI
pMOSFET model with body channel
A. Front surface depleted
The width of the body current path depends on the depth
of the depletion regions controlled by the front and the
back gates. The back depletion depth, dbx , can be
assumed to be constant along the channel [4, 7] and
equal to
a
fbbgb
obob
db qN
VV
cc
x
−
+⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+−= Si
2
SiSi 2ε
εε
. (1)
The front depletion depth at a certain point of the
channel can be written as
a
cfbfgf
ofof
df qN
VVV
cc
x
−−
+⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+−= Si
2
SiSi 2ε
εε
. (2)
In (1) and (2), ofc and obc are the front and back
oxide capacitances, Siε and aN are dielectric
permittivity and doping level, respectively, gfV and gbV
are the front and back gate voltages, respectively, and
cV is the channel voltage in a given point of the channel.
fbfV and fbbV are the front and back flat-band voltages.
We define the effective film thickness as
dbbb xtt −=eff, , where bt is the silicon film thickness.
Therefore, the body channel thickness at each channel
point is dfb xtx −= eff,ch . The mobile charge density in
the body channel is obtained as chxqNq abc = . The
threshold voltage fVth is defined at the minimum front
gate voltage that pinches off the channel at 0=cV , that
is [7]
Si
2
eff,eff,
th 2ε
ab
of
ab
fbff
qNt
c
qNt
VV ++= .
However, even when the whole silicon film is fully
depleted below the threshold, there is still a diffusion
current component (the subthreshold component) that
depends exponentially on fgf VV th− [8].
To develop a unified model, we have to consider
both the drift (that dominates above the threshold) and
the diffusion term (that dominates below threshold) of
the body current. We define the effective potential ψ in
order to extend (2) below the threshold, so that the
resulting bcq is written as
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
+⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ −
−= 2
Si2 bt
a
gft
btabc t
qN
V
tqNq ε
ψ
, (3)
where ofbbt ctt Sieff, ε+= , and fgfgft VVV th−= .
Hence, (3) is a generalization of (2) in which we
have replaced cV by the effective potential ψ in order
to extend the validity of the expression of bcq into the
subthreshold regime. In the subthreshold regime, bcq
depends exponentially on fgf VV th− [8]. So, ψ tends to
cV above the threshold, and in the subthreshold it tends
to a value that gives such dependence of bcq .
Therefore, the relationship between ψ and bcq is
bcbt
a
bc dqt
qN
q
d ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−−=
Si
1
ε
ψ . (4)
We write the body channel current as the sum of the
drift and diffusion terms
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
45
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−−=
dx
dq
v
dx
d
qWI bc
Tbcbbcd
ψ
μ , (5)
where bμ is the mobility in the silicon film, and
qkTvT = is the thermal voltage.
Using (3) in (4), we obtain the following expression
of the body channel current when the front surface is
fully depleted:
( )
( ) ( ) ,
2
3
1
,,
2
,
2
,
Si
3
,
3
,
Si
⎥
⎦
⎤
−−−−
⎢
⎣
⎡
−−=
sbcdbcTsbcdbc
bt
sbcdbc
a
bbcd
qqvqq
t
qq
qNL
W
I
ε
ε
μ
(6)
where sbcq , and dbcq , are the body channel mobile
charge densities at the source and drain ends,
respectively.
B. Front surface accumulated
When a portion of the front surface is in accumulation,
the accumulation charge density at a point of the surface
can be written as [7]
( )cfbfgfofac VVVcq −−−= . (7)
Writing the accumulation current as
( ) dxdVqWI cacacac −= μ ( acμ being the surface mo-
bility) and using from (7) ofacc cdqdV = we get
assuming the front surface is accumulated from source to
drain
( )
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
−= 2
,
2
,2
1
dacsac
of
acac qq
cL
WI μ , (8)
where dacq , and sacq , are the accumulation charge
densities at the source and drain ends, respectively,
obtained from (7).
When the front surface is fully accumulated,
neglecting the thickness of the accumulation layer, the
body current is written as
( ) ,,,
eff,
eff,
sacdac
of
ba
b
dsbabbcnd
qq
c
qtN
L
W
VtqN
L
WI
−=
=−=
μ
μ
(9)
where ‘bcnd’ index stands for ‘Body Current at Non-
Depleted front surface’, and dsV is the drain-source
voltage.
C. Front surface partly accumulated, partly depleted
To develop a unified model, we have to assume that
there can be a portion of the channel with accumulation
at the surface (from the source, 0=x , to a length
1Lx = , see Fig. 1b) and a portion with depletion at the
surface (from 1Lx = to the drain, Lx = ). By
integrating the drift-diffusion equation from source to
drain, we obtain
∫
∫∫
−+
+−−=
L
L
bcbcTb
L
Cbabacac
L
ds
dqdqW
dVtqNqWdxI
1
1
.)(
)(
0
eff,
0
ψνμ
μμ
(10)
To integrate, we make the following variable
changes: between 0=x and 1Lx = we can write
ofacc cdqdV = from (7). Between 1Lx = and Lx = ,
we can write bcbta dqtqNd ))(/1 Si −−= εψ from (4). To
obtain an analytical solution, we assume that the
effective mobilities bμ and acμ are independent of the
position on the channel (as we will discuss below, acμ
depends on the applied voltages).
We get
( )
( )
( )
( ) ( )⎥
⎦
⎤
−−−−
⎢
⎣
⎡
−−+
+−+
+
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
−=
pbcdbcTpbcdbc
bt
pbcdbc
a
b
sacpac
of
ba
b
pacsac
of
acd
qqvqqt
qq
qNL
W
qq
c
qtN
L
W
qq
cL
WI
,,
2
,
2
,
Si
3
,
3
,
Si
,,
eff,
2
,
2
,
2
3
1
2
1
ε
ε
μ
μ
μ
(11)
where pbcq , and pacq , are the quasi-neutral and
accumulation charge densities at 1Lx = , respectively.
Therefore, 0, =pacq and ff,, ebapbc tqNq = .
Eq. (11) can be extended to all the possible regimes
(including the surface accumulated from the source to
drain and that depleted from the source to drain)
replacing pacq , by dacq , and pbcq , by sbcq , :
( )
( )
( )
( ) ( ) .
2
3
1
2
1
,,
2
,
2
,
Si
3
,
3
,
Si
,,
eff,
2
,
2
,
⎥
⎦
⎤
−−−
⎢
⎣
⎡
−−+
+−+
+
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
−=
sbcdbcTsbcdbc
bt
sbcdbc
a
b
sacdac
of
ba
b
dacsac
of
acd
qqvqq
t
qq
qNL
W
qq
c
qtN
L
W
qq
cL
W
I
ε
ε
μ
μ
μ
(11')
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
46
When the front surface is accumulated from the
source to 1Lx = , 0, =dacq and eff,, basbc tqNq = , and
therefore, (11') gives (11). When the front surface is
accumulated from surface to drain,
eff,,, badbcsbc tqNqq == , and (11') reduces to
bcndacds III += as it should. When the front surface is
depleted from the source to drain 0,, == dacsac qq , and
(11') reduces to bcdds II = as it should, too.
Therefore, we can write bcdbcndacds IIII ++=
provided acI , bcndI and bcdI are written as (6), (8) and
(9), respectively. Please, note that this does not mean
that the total channel current is considered as the sum of
three components in parallel; in fact these two
components of the body current appear in series, but
they are not written as (6) nor (9), because one
component flows in a length equal to 1L and the other
one flows in that equal to 1LL − .
D. Continuous expressions
To further develop the unified single-piece model, we
need to approximate unified expressions for accumu-
lation and quasi-neutral (body) charges at source and
drain ends sacq , , dacq , , sbcq , , and dbcq , , respectively, valid
from the subthreshold to total accumulation regime. We
introduced the effective potential ψ in (3) for that. As an
explicit expression, we use a suitable interpolation
function gfteV instead of ψ−= gftgfti VV . Above the
threshold, when cfbfgf VVV += , this interpolation function
should smoothly give eff,babc tqNq = . So, we have the
following expression for the quasi-neutral mobile charge
density:
2
Si2gfte
bc a bt bt
a
V
q qN t t
qN
ε
⎡ ⎤⎛ ⎞
⎢ ⎥= − +⎜ ⎟
⎢ ⎥⎝ ⎠⎣ ⎦
(12)
and
( )[ ]( )
[ ]( ) ⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
+
−+
−=
PS
pegftePS
pegfte A
VVA
VV
exp1log
1exp1log
1 0 , (13)
where ffbfpe VVV th−= , PSA in (3) is a fitting
parameter that controls the transition from depletion to
diffusion of the depleted charge in an AM SOI
pMOSFET, it makes 1)exp( >>PSA , and 0gfteV is the
following interpolation function:
( ) 2
00
2
0 4 gfteTTgfte VnvnvV +−= , (14)
where
( ) ( )
.
2
exp
2
exp
1log
2
0
00
⎟
⎟
⎠
⎞
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡ −−
+
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡ −−
+
⎜
⎜
⎜
⎝
⎛
+−=
NTT
cgft
T
cgft
NTT
NTTgfte
Snv
VV
nv
VV
Snv
v
SnvV
(15)
NTS ( 1< ) is the parameter that controls the transition
from below to above threshold, 0v is a fitting parameter
that controls the magnitude of the body charge density
above the threshold, and n corresponds to the
subthreshold slope.
Above the threshold and below the flat band
( cfgfcfbf VVVVV +<<+ th ), pegfte VV >0 and
cgftgftegfte VVVV −≅≅ 0 , as it should; below threshold,
still pegfte VV > and 0gftegfte VV ≅ , but from (14) and
(15) we get that to the first order 0gfteV is proportional to
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
−
T
cgft
nv
VV
exp ; substituting (14) in (13) we obtain
from (12) that bcq is, to the first order, proportional to
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
−
T
cgft
nv
VV
exp , as it should. Above the flat band
pegfte VV <0 (note that for SOI pMOSFET 0gfteV and
peV are both negative) and hence pegfte VV ≅ and
eff,babc tqNq ≅ , as it should.
In the expression for bcdI (6), we calculate sbcq , and
dbcq , from Eqs (12)-(15) for cV equal to the source
voltage sV and to the drain voltage dV , respectively,
therefore bcdI tends smoothly to the desired limits in the
different regimes.
The diffusion term – the latter term in Eq. (6) – only
dominates in the subthreshold regime. Due to intrinsic
overestimation in the calculation of bcq by using
Eq. (12), which can affect the near-threshold regime, we
modify (6) by using, instead of Tv , the factor
)(1 00
0
Td,gfteTs,gfte
T
T vVvV
v
v
+−
= , where sgfteV ,0 and
dgfteV ,0 are calculated from Eq. (14) at sc VV = and
dc VV = , respectively. Therefore, TT vv ≅0 in the
subthreshold, as it should, and it tends to zero above the
threshold. This modification improves the accuracy near
the threshold.
For the accumulation charge density, we present a
useful unified expression that does not require
interpolation functions more than those used to calculate
sbcq , and dbcq ,
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
47
( )gftegfteofac VVcq −−= 0 . (16)
It is clear that (16) tends to the desired limits in all
regimes. Below the flat band 0gftegfte VV ≅ and 0=acq .
Above the flat band pegfte VV = and
cfgftgfte VVVV −−= th0 and, hence,
( )cfbfgfofac VVVcq −−−= , as it should.
Calculating sacq , and dacq , from (16) with sc VV = and
dc VV = , we get an explicit ∞C -continuous model for
acI and bcndI . Therefore, bcdbcndacds IIII ++= is
the expression of the total channel current in all regimes.
2.2. Second-order effects
Here we improve the model by including the second-
order effects such as vertical and lateral field effects,
channel-length modulation and series resistance [2].
Generally, influence of such effects is not very important
at the used channel length, but it could be noticeable at
large drain voltages (in the saturation regime), and
become much more significant with decreasing the
channel length. In this subsection, we describe briefly
the main second-order corrections used in the model [2].
A. Vertical field effect
In the above analysis, we have not considered the
degradation of the surface mobility along the channel.
However, we can keep the same equations using an
effective surface mobility eff,acμ which accounts for
mobility degradation with the average normal field in the
accumulation channel. A useful expression for mobility
degradation is
sf
ac
ac
Eα
μ
μ
+
=
1
eff, , (17)
where ( ) Si,, 2εdacsacsf qqE += is the average field
along the channel of the normal in the accumulation
layer.
There is no degradation of the body mobility bμ ,
since the normal field is low in the body region.
B. Lateral field effect
However, both the body and surface components of the
current are affected by the velocity saturation effect. We
assume that the drift velocity of charge carriers in the body
can be written as ( ) [ ]( )dxdvdxdv bb ψμψμ sat21−=
if bvdxd μψ sat2< and as satvv = if
bvdxd μψ sat2> , where satv is the saturation velocity.
Following the same procedure as in Section 2.1, but
integrating the drift-diffusion equation from 0=x to
effLx = ( effL being the effective length where the
gradual channel approximation is valid, i.e.,
bvdxd μψ sat2< ; we will define this length later), we
finally get the same expression of the body current
bcndbcd II + as in the Section 2.1, but with bμ replaced
by ( )bLdseb VV ,1−μ , where bbL LvV μeffsat, 2= , and
dseV is the effective drain-source voltage. Assuming the
same velocity-field relationship for the surface compo-
nent, acI has the same expression as in Section 2.1, but
with acμ replaced by ( )acLdseac VV ,eff, 1−μ , where
eff,effsat, 2 acacL LvV μ= .
dseV is defined as an interpolation function that tends
to dsV in the linear regime and to saturation voltage
satdV in the saturation one:
( )[ ]( )
[ ]( ) ⎥
⎦
⎤
⎢
⎣
⎡
+
−+
−=
TS
ddsTS
ddse A
VVA
VV
exp1log
1exp1log
1 sat
sat , (18)
where TSA is a fitting parameter that controls the
transition from the linear regime to saturation. In the
subthreshold, the effect of saturation velocity is
negligible and dseV should tend to zero.
The saturation voltage is defined as the drain-source
voltage, at which in the quasi-neutral region the carriers
travel at a constant velocity, the saturation velocity satv .
It is obtained by equating the expression of dsI to
eff,sat bads tqNWvI = . In our case, it cannot be found
analytically, so we use a special approximation again,
valid in all operation regimes owing to the use of the
interpolation function (14)
bt
VVds
Tsgfte
sgfte
sgfted tWv
I
vV
V
VV sgftedse
Sisat,0
,0
,0sat
,0
ε
=
−
−= , (19)
where
sgftedse VVdsI
,0= is the unified expression of the
drain current at sgftedse VV ,0= (that is, when dbcq , and
dacq , are negligible). satdV tends to sgfteV ,0 in the
subthreshold, which allows to get the desired expression
of dbcq , , and above the threshold it tends to the desired
saturation voltage.
C. Channel length modulation
When the body conduction is in the saturation regime,
the channel length modulation effect has to be accounted
for. We write sateff lLL −= , where satl is the modulated
channel length:
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
48
⎟⎟
⎟
⎠
⎞
⎜⎜
⎜
⎝
⎛ ++
=
2
2
2
2
11
sat log
c
ccc
ll d , (20)
where dseds VVc −=1 , bd vlc μsat2 = , and dl is the
characteristic length that is considered as adjustable
parameter.
D. Series resistance
The effect of the series drain and source resistance is
included to the first order by a multiplication factor:
idRd IfI ,= , (21)
where idI , is the drain current expression without
accounting for the series resistance and
( )2111 RRR aaf ++= , where
, ,
1 ,eff tot 2
ac s ac d
R ac of
of
q qWa c R
L c
μ
⎛ ⎞+
= ⎜ ⎟⎜ ⎟
⎝ ⎠
, (22)
( )dbcsbcbR qq
L
WR
a ,,
tot
2 2
+= μ , (23)
and totR is the total parasitic drain-source resistance.
2.3. Fully-depleted AM SOI pMOSFET room-
temperature model
Here we consider the case of fully-depleted low-doped
AM SOI pMOSFET, deriving it from the FD EM SOI
nMOSFET model [3].
A. Overview of FD EM SOI nMOSFET room-
temperature model
The ∞C -continuous FD enhancement mode (EM) SOI
nMOSFET model [3] is based on the physical expression
for the mobile charge density in the front inversion
channel nfQ :
( ) ⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
+−= 2
2
24
11
TSof
nf
TSofnf
vnc
Q
vncQ , (24)
where Sn is the subthreshold slope ideality factor, and
2nfQ is a special approximation function:
.
2
exp
2
exp
4
11log
th
,th
2
⎥
⎥
⎦
⎤
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −−
+
⎢
⎢
⎣
⎡
+⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −−
+×
×−=
NTTS
cfgf
TS
cSifGf
NT
NTTSofnf
Svn
nVVV
vn
VnVV
S
SvncQ
(25)
In (25) the second term in the logarithm dominates in
weak inversion and the third one in strong inversion.
Here n stands for the body factor in strong inversion.
NTS controls the transition from weak to strong
inversion ( 1<NTS ). ifV ,th being the front threshold
voltage which corresponds to a surface potential of
cV+F2φ ( Fφ is the Fermi potential). While this
threshold value appears in a weak inversion term of (25),
a different value is introduced in the strong inversion
term, fVth , to take into account that the strong inversion
surface potential is always larger than cV+F2φ by a few
Tv . This capability to use two threshold voltages is an
advantage over other models, which have to artificially
overestimate the mobility degradation, especially for
moderate gfV , in order to account for the threshold
voltage increase from weak to strong inversion [9].
These two threshold voltages could be expressed as
gbifif VnVV )1(,0th,th −−= and gbff VnVV )1(0thth −−= ,
where ifV ,0th and 0th fV could be considered as fitting
parameters or derived from other technology parameters.
The interpolation function (24) tends to the desired
physically proper limits in weak and strong inversion
and yields continuous expression for the current:
( )
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡ −
−−=
of
snfdnf
snfdnfTnd nc
QQ
QQv
L
W
I
2
2
,
2
,
,,μ , (26)
where nμ is the electron mobility, snfQ , and dnfQ , are
the inversion charge densities at the source and drain
edges, calculated from (26) for cV equal to source
voltage sV and to drain voltage dV , respectively.
B. Customization for the case of FD low-doped AM SOI
pMOSFET
Therefore an explicit ∞C -continuous model for FD EM
nMOSFET is obtained in previous subsection. Here we
demonstrate that it can be customized for the case of FD
low-doped AM pMOSFET by appropriate change of
voltage signs. Other device type dependent parameters,
such as surface potentials, zero for weak accumulation
and a few Tv lower for strong accumulation, are fully
encapsulated in the two threshold voltages ifV ,0th and
0th fV , which could be considered as fitting parameters
again, or calculated from technological parameters of
AM pMOSFET devices following [10]:
th 0, 2 2
a b bb a b
f i fbf fbb
of of ob
qN t c qN tV V V
c c c
⎛ ⎞
= + − − −⎜ ⎟
⎝ ⎠
, (27a)
th 0 th 0,f f i S saV V n φ= + . (27b)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
49
Here bbc is the capacitance of the film and the back
oxide in series, ( )obbobbbb ccccc += , where
bb tc Siε= is the film capacitance, and saφ is the
surface potential of strong accumulation. Now we can
use ifV ,th and fVth in (25) with appropriate change of
signs.
The second-order effects are introduced similarly as
described in Section 2.2, for details please refer the
original paper [3].
2.4. Developing of high-temperature model
A. General temperature dependences
Due to the fact that the ∞C -continuous model described
above was developed on physical principles and depends
only on physical parameters of the device, there is clear
possibility to introduce temperature dependences of all
the parameters. Temperature dependences of all the main
parameters of AM SOI pMOSFET (intrinsic carrier
concentration in , bandgap width gE , mobility μ , etc.)
are well-known [11]. However, this is not enough to
develop the high-temperature model, because some
assumptions of the described above model are not valid
at high temperatures.
B. Subthreshold slope at high temperatures
The main problem is that the potential distribution in the
film at high temperatures differs significantly from the
potential distribution at room temperature, and the
charge-sheet model approximation which is used in the
∞C -continuous models [2, 3] described in the previous
sections becomes inaccurate [12]. As a result, we have
considerable disagreement between the model and
experimental curves in the subthreshold and off-state
regions, while off-state currents at high temperatures
becomes extremely large and can influence the normal
operation of devices, so proper modeling of them is
necessary. The models like [2, 3] described above
predict linear behavior of the subthreshold slope
dependence upon temperature, while our experiment
states that this dependence is highly nonlinear. This was
explained using numerical simulation by prevalence of
diffusion component of current [12]. Instead of
numerical simulations, we used an empirical dependence
extracted from experimental data: a combination of 3rd
power polynomial and exponential dependences (see
Fig. 2):
43
3
2
300
1 e CTCTCCS T +++= − , (28)
with the coefficients 1
1 V41.2 −=C ,
318
2 KV1007.4 −−−⋅−=C , 11
3 KV01.0 −−−=C and
1
4 V23.2 −−=C .
C. High-temperature off-state currents
We consider two components of the off-state leakage
currents in the accumulation mode p-channel device:
current due to the thermal generation in the body film
bulk (diffusion current) and current due to the thermal
generation in the drain-depleted body film region
(generation current).
The diffusion component is expressed as [11]
( )
c
b
a
ivV
Tbosd L
Wt
N
qn
vI TD
2
e1−= μ , (29)
where cL is the diffusion length (or the effective device
length if the latter is shorter). As it was showed
previously [12], the total carrier density responsible for
the diffusion component in the case of accumulation
mode p-channel devices is the same as in the case of the
enhancement mode n-channel ones, so we used common
approximation for minority carrier density
a
i
N
qn2
.
The generation current in the depleted region of the
body near the drain is expressed as [11]
bi
g
i
osg tWL
qn
I
τ
= , (30)
where
⎪⎭
⎪
⎬
⎫
⎪⎩
⎪
⎨
⎧
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−−⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
i
a
T
D
i
a
a
T
i n
N
v
qV
n
N
N
v
L lnln
2 Siε
, (31)
iL stands for the depth of depleted region near the drain,
where the thermal generation rate is maximal and
outside of it the rate is negligible, gτ is the generation
lifetime.
Therefore, the total off-state current is
osgosd III +=off . (32)
3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0
0 . 0 5
0 . 1 0
0 . 1 5
0 . 2 0
0 . 2 5
0 . 3 0
0 . 3 5
Drain
voltage
-0.1V
Backgate
voltage 0V
Su
bt
hr
es
ho
ld
s
w
in
g
(d
ec
V
-1
)
Temperature (K)
symbols - experiment
line - empirical model:
S = 2.41exp(T/300)-4.07x10-8T3 - 0.01T-2.23
Fig. 2. Empirical dependence of the subthreshold slope upon
temperature derived from experimental data.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
50
- 3 . 5 - 3 . 0 - 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0 0 . 5
0 . 0
0 . 5
1 . 0
1 . 5
2 . 0
2 . 5
-0.05V
-2V
Drain
voltage
0V
-1.5V
Backgate
voltage
+1.5V
D
ra
in
c
ur
re
nt
(
mA)
Front-gate voltage (V)
(a)
symbols - experiment
lines - model
- 3 . 5 - 3 . 0 - 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0 0 . 5
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
-0.05V
-2V Drain
voltage
0V
-1.5V
Backgate
voltage
+1.5V
D
ra
in
c
ur
re
nt
(
mA)
Front-gate voltage (V)
(b)
symbols - experiment
lines - model
Fig. 3. Results of modeling the transfer characteristics ( gdVI ) at room temperature for various back-gate biases in the linear (a)
and saturation (b) regimes.
3. Results and discussion
3.1. Fully-depleted AM SOI pMOSFET room-
temperature model
The obtained model was validated using experimental
data, obtained for AM SOI pMOSFET devices,
fabricated on UNIBOND material in DICE, UCL
(Belgium). The devices possessed the following
parameters: the front gate oxide, film and BOX
thicknesses were 308, 889 and 4000 Å, the channel
doping was 316 cm162 −× only, and the channel length
and width were L = W = 20 μm. Temperature
measurements were performed up to 300 °C. Due to low
doping of the Si film, we have the case of fully-depleted
AM SOI pMOSFET.
Using the model, it is possible to find values of
device parameters by fitting the model curve to
experimental data. For this aim, the method of Fast
Simulated Diffusion was used [13], especially developed
for resolving of multidimensional minimization
problems like MOSFET modeling is. The found values
of main parameters at room temperature are shown in
Table. The model also accounts the effect of decreasing
the device length and width during technological
processes of device manufacturing, i.e., doping of the
source and drain region and forming the side oxides. The
appropriate corrections, lateral diffusion length for the
channel length, and diffusion width for the width were
determined and listed in Table.
In Fig. 3, we demonstrate the comparison of the
experimental and model curves of the transistor transfer
characteristics ( gdVI ) at room temperature both in linear
(drain voltage V05.0−=dsV , see Fig. 3a) and saturation
( V2−=dsV , see Fig. 3b) regimes of operation for
different back-gate bias voltages. In Fig. 4, we compare
the same curves in the logarithmic scale to see the results
of modeling in the subthreshold region. It is clearly seen
that the model shows a good agreement with
measurements in all the regions from subthreshold
(Fig. 4) to above threshold voltages (Fig. 3) both in
linear and saturation regimes.
Table. Determined values of MOSFET parameters and
their temperature dependences.
Parameter Room-temp.
value
Temperature dependence(11)
(parameters refitted)
Weak accumulation
threshold voltage,
r
i
V
,0th
, V
−0.38 ( )room
3
,0th,0th 10 TTVV r
ii −+= −
Strong
accumulation
threshold voltage,
rV
0th
, V
−0.41 the same
Hole mobility,
m2/(V⋅s)
- in accum. channel,
0acμ
0.0211 ( ) 6.1
room0
−= TTμμ
- in body channel,
0bμ
0.0291
Field mobility degr.
factor, 0fα , m/V
81065.1 −× ( ) 05.2
room0
−= TTff αα
Lateral diffusion
length, latl , m
71068.8 −×
Diffusion width,
dw , m
61016.1 −×
Source/drain series
resist., totR , Ohm
220
Saturation rate,
0satv , m/s
4100.8 × ( )
( )room
0satsat 2/exp8.01
2/1exp8.01
TT
vv
+
+
=
Characteristic
length, dl , m
81009.2 −×
Generation lifetime,
0gτ , s
7109.0 −× ( )TTg
64.213 1013.1cosh10 −− ×=τ
Recombination
lifetime, 0rτ , s
6101.0 −× ( ) 7.2
room0 TTrr ττ =
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
51
- 3 . 5 - 3 . 0 - 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0
0
1
2
3
4
5
200°C
300°C
100°C
-0.1V
-2V
Drain
voltage
30°C
Backgate
voltage 0V
D
ra
in
c
ur
re
nt
(
mA)
Front-gate voltage (V)
(a)
symbols - experiment
lines - model
temperature
- 3 . 5 - 3 . 0 - 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0
0
1 0
2 0
3 0
4 0
5 0
6 0
200°C
300°C
100°C
-0.1V
-2V
Drain
voltage
30°C
Backgate
voltage 0V
D
ra
in
c
ur
re
nt
(
mA)
Front-gate voltage (V)
(b)
symbols - experiment
lines - model
temperature
Fig. 6. Transfer characteristics ( gdVI ) at high temperatures for
zero back-gate bias in the linear (a) and saturation (b) regimes.
- 3 - 2 - 1 0 1 2
1 0
- 1 2
1 0
- 1 1
1 0
- 1 0
1 0
- 9
1 0
- 8
1 0
- 7
1 0
- 6
1 0
- 5
-0.05V
-2V
Drain
voltage
D
ra
in
c
ur
re
nt
(A
)
Front-gate voltage (V)
symbols - experiment
lines - model
0V
-1.5V
Backgate
voltage: +1.5V
Fig. 4. Transfer characteristics ( gdVI ) at room temperature for
various back-gate biases in the subthreshold region.
In Fig. 5, we compare the model and measured
output characteristics ( ddVI ) at room temperatures. One
can observe a good agreement for all the regimes of
operation, from the linear to saturation ones.
3.2. High-temperature simulations
With regards to the main result of this work, i.e.,
modeling the high-temperature AM MOSFET
characteristics, the temperature dependences of the main
model parameters are presented in Table.
Fig. 6 shows a comparison of the measured and
model gdVI curves for AM SOI pMOSFET at high
temperatures. As one can see, modeled characteristics
show a good agreement with experimental results in the
wide range of temperatures (from the room temperature
up to 300 °C) in linear (Fig. 6a) and saturation (Fig. 6b)
regimes. A very important feature for analog design, i.e.
the zero-temperature coefficient (ZTC) point,
corresponding to a constant gdVI bias point with
temperature, is particularly well modeled, too.
- 3 . 0 - 2 . 5 - 2 . 0 - 1 . 5 - 1 . 0 - 0 . 5 0 . 0
0
2
4
6
8
1 0
1 2
-0.6V
-0.3V
Frontgate
voltage
-1.2V
-1.5V
Backgate
voltage 0V
-0.9VD
ra
in
c
ur
re
nt
(
mA)
Drain voltage (V)
symbols - experiment
lines - model
Fig. 5. The output characteristics ( ddVI ) at room temperature
for zero back-gate bias.
The same characteristics, depicted in the logarithmic
scale in Fig. 7a, show the behavior of the model curves
in the subthreshold and off-state regions. As one can see,
the subthreshold swing dependence upon temperature is
very good. The model curves exhibit smooth transition
between all the regimes of operation (from the off-state
through subthreshold to the above threshold region).
Also, the off-state current temperature dependence is
correctly modeled. In Fig. 7b, we have more vivid
picture of this dependence. The model curves demon-
strate proper quantitative and qualitative description of
the off-state current dependence upon temperature. As it
should be expected, we have significant difference
between the saturation and linear off-state currents at
low temperatures, which is explained by increasing the
generation current (30) at high absolute values of the
drain voltage, because of increasing the depth of the
depleted region near the drain [see Eq. (31)], where
generation takes place. At the same time, the diffusion
component of the off-state current (29) tends to saturate
with the drain voltage. Concerning the temperature
dependence of both components of leakage current, the
generation component (30) increases with temperature as
)(Tni , while the diffusion one (29) varies as )(2 Tni . At
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
52
- 3 - 2 - 1 0 1 2
1 0
- 1 3
1 0
- 1 2
1 0
- 1 1
1 0
- 1 0
1 0
- 9
1 0
- 8
1 0
- 7
1 0
- 6
1 0
- 5
200°C
300°C
100°C
-0.1V
-2V Drain
voltage
30°C
Backgate
voltage 0V
D
ra
in
c
ur
re
nt
(A
)
Front-gate voltage (V)
(a)
symbols - experiment
thick lines - linear model
thin lines - saturation model
temperature
3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0
1 0
- 1 4
1 0
- 1 3
1 0
- 1 2
1 0
- 1 1
1 0
- 1 0
1 0
- 9
1 0
- 8
Frontgate
voltage 1.5V
-0.1V
-2V
Drain
voltage
Backgate
voltage 0V
O
ff-
st
at
e
dr
ai
n
cu
rre
nt
(A
)
Temperature (K)
(b)
symbols - experiment
lines - model
Fig. 7. Transfer characteristics ( gdVI ) at high temperatures for
zero back-gate bias in the subthreshold region (a) and the off-
state current vs temperature (b).
3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0
- 0 . 5
- 0 . 4
- 0 . 3
- 0 . 2
- 0 . 1
0 . 0
Drain voltage
-0.1V
Backgate
voltage 0V
Th
re
sh
ol
d
vo
lta
ge
(V
)
Temperature (K)
(a)
symbols - experiment
line - model
- 3 - 2 - 1 0 1 2
0
1
2
3
4
5
- 4
0
4
8
x 1 0
- 6
(b)
Threshold
position
2nd derivative
Drain
voltage
-0.1V
Backgate
voltage 0V
D
ra
in
c
ur
re
nt
(
mA)
Front-gate voltage (V)
Experimental Id-Vg
Room
temperature
d
2 I d/d
V2 g (
AV
2 )
Fig. 8. Comparison of the experimental and model
dependences for the threshold voltage upon temperature for
zero back-gate bias (a) and an illustration of the 2nd derivative
method for determining the threshold voltage (b).
high temperatures the diffusion current increases
significantly, and it becomes the dominant component of
the leakage current. Therefore, the difference between
off-state currents in the saturation and linear regimes
caused by the generation component becomes slighter at
high temperatures, as clearly seen from Fig. 7b. The
same feature of leakage current behavior at high
temperatures was reported previously [12].
In Fig. 8a, comparing the experimental and model
threshold voltage dependences upon temperature is
presented. The experimental values of the threshold
voltage were obtained from the experimental gdVI
curves by using the 2nd derivative method [14] (simple
illustration of the method is depicted in Fig. 8b). Model
curves are straight lines according to the chosen
dependence of the threshold voltage upon temperature,
and taking the dispersion of experimental values into
consideration, model curves show a good coincidence
with the experimental ones (Fig. 8a).
The important analog parameter dm Ig ( mg being
the transconductance gfdm dVdIg = ) for different
temperatures is plotted in Fig. 9. When the value of
dm Ig is the largest ones, the maximum voltage gain of
a MOSFET is obtained [7]. As Fig. 9a shows, the
maximum of this parameter is getting lower with
increase of temperature, due to the degradation of
subthreshold operation, which infers that the maximum
voltage gain of the device is significantly decreased.
Nevertheless, when biasing the devices at the ZTC point,
to maintain constant bias with temperature for analog
circuits such as amplifiers [15], we observe and correctly
model a much reduced degradation of the dm Ig
coefficient with temperature (Fig. 9b).
The gate-source intrinsic capacitance
( sggs dVdQC −= ) measurements at the temperature
300 °C compared to the model curves are plotted in
Fig. 10. Experimental data were taken from the data for
the transistor with the front gate oxide, film and BOX
thicknesses of 550, 1000 and 4200 Å, the channel
doping of 316 cm108 −× , and with the channel length and
width of μm20 [4]. There is also a good agreement
through all the regimes for different values of the drain
voltage.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 1. P. 43-54.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
53
1 0
- 1 5
1 0
- 1 3
1 0
- 1 1
1 0
- 9
1 0
- 7
1 0
- 5
- 1 0
0
1 0
2 0
3 0
4 0
(a)
200°C
300°C
100°C Drain
voltage
-0.1V
30°C
Backgate
voltage 0V
g m
/I d (
1/
V)
Drain current Id (A)
symbols - experiment
lines - model temperature
3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0
2
3
4
5
6
7 Section at ZTC point
(current level 3.4x10-7A)
Frontgate
voltage -0.6V
(b)
-0.1V
Drain
voltage
Backgate
voltage 0V
g m
/I ds
(1
/V
)
Temperature (K)
symbols - experiment
lines - model
Fig. 9. Results of modeling the transconductance ( dm Ig vs
dI ) at high temperatures (a) and a section of this dependence
at ZTC point (b).
- 4 - 2 0
0 . 0 0
0 . 0 2
0 . 0 4
0 . 0 6
0 . 0 8
0 . 1 0
0 . 1 2
0 . 1 4
0 . 1 6
0 . 1 8
Source
voltage 0V
-1V
-0.05V
-4V
Drain
voltage
Backgate
voltage 0V
G
at
e-
so
ur
ce
c
ap
ac
ita
nc
e
(p
F)
Front-gate voltage (V)
symbols - experiment
lines - model
Fig. 10. Gate-source intrinsic capacitance ( gsC vs gfV ) at the
high temperature (300 °C).
4. Conclusions
The high-temperature AM SOI p-MOSFET model has
been developed in the paper. The model is based on the
approximate ∞C -continuous expressions of the
accumulation and quasi-neutral charge densities. The
obtained agreement between the model and experimental
data for AM SOI p-MOSFET characteristics is very
good. We specifically developed new formulations for
the subthreshold slope and off-state currents. The model
works properly in all the operation regimes including
subthreshold and off-state conduction in the range from
the room temperature up to 300 °C. A smooth transition
between different operation regimes, as well as proper
modeling the AC and DC MOSFET characteristics
(ZTC, transconductance-to-drain current ratio, intrinsic
capacitances) is demonstrated, which allows to use the
model for high-temperature analog circuits simulations.
Acknowledgements
The work was performed in the frame of SPRING
project (project #IST-1999-12342), and also was
partially supported by NATO CLG (PST CLG 979999).
The authors are thankful to T.E. Rudenko, V. Kilchytska
and A. Tuor for helpful discussions.
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