A silicon carbide thermistor
We consider a silicon carbide thermistor with multilayer Au–TiBx–Ni2Si ohmic contacts intended for operation in the 77 to 450 K temperature range.
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Cite this: | A silicon carbide thermistor / N.S. Boltovets, V.V. Kholevchuk, R.V. Konakova, Ya.Ya. Kudryk, P.M. Lytvyn, V.V. Milenin, V.F. Mitin, E.V. Mitin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 67-70. — Бібліогр.: 5 назв. — англ. |
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Boltovets, N.S. Kholevchuk, V.V. Konakova, R.V. Kudryk, Ya.Ya. Lytvyn, P.M. Milenin, V.V. Mitin, V.F. Mitin, E.V. 2017-06-15T03:38:29Z 2017-06-15T03:38:29Z 2006 A silicon carbide thermistor / N.S. Boltovets, V.V. Kholevchuk, R.V. Konakova, Ya.Ya. Kudryk, P.M. Lytvyn, V.V. Milenin, V.F. Mitin, E.V. Mitin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 67-70. — Бібліогр.: 5 назв. — англ. 1560-8034 PACS 84.32.Ff https://nasplib.isofts.kiev.ua/handle/123456789/121636 We consider a silicon carbide thermistor with multilayer Au–TiBx–Ni2Si ohmic contacts intended for operation in the 77 to 450 K temperature range. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics A silicon carbide thermistor Article published earlier |
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A silicon carbide thermistor |
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A silicon carbide thermistor Boltovets, N.S. Kholevchuk, V.V. Konakova, R.V. Kudryk, Ya.Ya. Lytvyn, P.M. Milenin, V.V. Mitin, V.F. Mitin, E.V. |
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A silicon carbide thermistor |
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A silicon carbide thermistor |
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A silicon carbide thermistor |
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A silicon carbide thermistor |
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silicon carbide thermistor |
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Boltovets, N.S. Kholevchuk, V.V. Konakova, R.V. Kudryk, Ya.Ya. Lytvyn, P.M. Milenin, V.V. Mitin, V.F. Mitin, E.V. |
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Boltovets, N.S. Kholevchuk, V.V. Konakova, R.V. Kudryk, Ya.Ya. Lytvyn, P.M. Milenin, V.V. Mitin, V.F. Mitin, E.V. |
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2006 |
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English |
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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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We consider a silicon carbide thermistor with multilayer Au–TiBx–Ni2Si ohmic contacts intended for operation in the 77 to 450 K temperature range.
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1560-8034 |
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https://nasplib.isofts.kiev.ua/handle/123456789/121636 |
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A silicon carbide thermistor / N.S. Boltovets, V.V. Kholevchuk, R.V. Konakova, Ya.Ya. Kudryk, P.M. Lytvyn, V.V. Milenin, V.F. Mitin, E.V. Mitin // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 4. — С. 67-70. — Бібліогр.: 5 назв. — англ. |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 67-70.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
67
PACS 84.32.Ff
A silicon carbide thermistor
N.S. Boltovets1, V.V. Kholevchuk2, R.V. Konakova2, Ya.Ya. Kudryk2, P.M. Lytvyn2,
V.V. Milenin2, V.F. Mitin2, E.V. Mitin2
1State Enterprise Research Institute “Orion”, 8a, Eugene Pottier str., 03057 Kyiv, Ukraine
2V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine
Phone:(380-44) 525-61-82; fax: (380-44) 525-83-42
E-mail: konakova@isp.kiev.ua
Abstract. We consider a silicon carbide thermistor with multilayer Au–TiBx–Ni2Si
ohmic contacts intended for operation in the 77 to 450 K temperature range.
Keywords: silicon carbide, thermistor, ohmic contact, buffer layer.
Manuscript received 04.10.06; accepted for publication 23.10.06.
1. Introduction
Silicon carbide (SiC) is a promising material for device
applications (in particular, those involving arduous
environmental conditions), and its thermal and radiation
resistances are well documented. The SiC devices are
usually used for extreme electronics when high
temperatures and intense radiation are present.
The main subject of this work was the
implementation of SiC for development of a highly
sensitive thermometer capable for use from liquid
nitrogen temperatures up to 450 K and in the presence of
ionizing radiation.
It is well known that the radiation and thermal
tolerances of semiconductor devices strongly depend on
their design and the material properties, especially on the
radiation and thermal resistances of the electrical
contacts to the semiconductor elements. The preparation
of reliable ohmic metal contacts to semiconductors
operating at high temperatures or under radiation
presents a difficult materials science problem. In the
course of operation both under high radiation and in high
temperature environment, the main mechanism of
contact degradation is due to the mass transfer from the
metal layer into the semiconductor element structure.
The process of contact degradation may change the
resistance and thermal sensitivity of sensors. Usually
structure defects which are also produced by radiation in
doped semiconductors have a small effect on the thermal
sensor properties; they can strongly affect the sensor
properties only after very high dose of irradiation.
The ohmic contacts must therefore be chemically
and physically compatible with the thermo-sensitive
material over the operating temperature range and have
similar resistance to the measurement environment of
the thermometer. In the case of SiC thermometers, the
formation of such contacts makes a considerable
physico-technological problem since many of the
metallic materials which are traditionally used as ohmic
contacts form carbides and silicides when interacting
with SiC, thus leading to nonuniform metal−SiC
interfaces. As a result, the contacts are degrading in the
course of operation at high temperatures. The
degradation processes result in mass transfer of gold
from the metallization layer into SiC through non-
uniform metallic phase layers in the ohmic contact.
Here we present our results on development of a
SiC thermistor with multilayer Au–TiBx–Ni2Si ohmic
contacts. A buffer layer (TiBx) was formed between the
upper (Au) metallization layer and metal layer (Ni2Si)
forming the ohmic contact. This buffer layer is made by
a quasi-amorphous nanocrystalline TiBx phase that
prevents mass transfer in contacts.
2. Sample preparation and experimental procedures
In our experiments, we used Lely-grown SiC single
crystals of п-type (polytype 21R). The concentration of
non-compensated donors was ~1.2⋅1018 cm-3. After
chemical treatment of surface, nickel layers (thickness of
200 nm) were deposited onto both SiC faces by using
magnetron sputtering. Then these layers were fired at the
temperature Т = 1000 °C for 90 s. After this, using
magnetron sputtering, we deposited layers of TiBx
(100 nm thick) and gold (200 nm thick) onto the ohmic
contacts formed by the above way. The gold layer was
then developed up to a thickness of 3 μm with
electroplating. The scribed chips (area of 0.5×0.5 mm2)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 67-70.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
68
0 5 10 15
0
20
40
60
80
100 C
Au
O
B
Ti
Si
Ni
At
. %
t, min
a)
0 5 10 15
0
20
40
60
80
100 C
Au
O
B
Ti
Si
Ni
At
. %
t, min
b)
Fig. 1. Auger concentration depth profiles of Au–TiBx–Ni–
n-SiC contact components before (a) and after RTA (b) at
1000 °C .
were mounted into packages. After this, we took the
thermometric characteristics of thermistors in the
77−450 K temperature range.
Both before and after metal−SiC structure firing,
we measured (i) metal−SiC contact resistance of the test
structures obtained and (ii) concentration depth profiles
of contact components using the Auger electron
spectroscopy (AES). Phase composition of the ohmic
contacts was determined with X-ray diffraction (XRD)
technique. The thermometric characteristics of the Au–
TiBx–Ni2Si–n-21R-SiC system were measured within
the 77−450 K temperature range.
3. Results and discussion
А. Characterization of Au–TiBx–Ni–21R-SiC contacts
For the Au–TiBx–Ni–21R-SiC test structures, we
measured the Auger component concentration depth
profiles in the metallization layers and at the Ni–n-21R-
SiC interface, both before and after rapid thermal
annealing (RTA) at 1000 °С (Fig. 1a, b). One can see
from Fig. 1a that the initial sample retains the layered
metallization structure, and the Ni–n-21R-SiC interface
has a junction region formed with the components of the
semiconductor and TiBx (whose composition is close to
TiB2). According to the data from literature [1], one can
assume that the junction region at the Ni–n-21R-SiC
interface is formed with the low-temperature nickel
silicide phases. (This contact region is considered in
more detail in the subsection B.)
No considerable changes occurred in the Au and
TiB2 layers after RTA at Т = 1000 °С. The contact-
forming Ni layer, however, changed its structure due to
reaction with SiC.
A comparison between the metallization
component concentration depth profiles taken before and
after RTA showed that the TiB2 layer demonstrates
buffer properties. In the course of RTA at Т = 1000 °С,
TiB2 practically did not react with the contact-forming
layer formed with nickel silicides. The Au–TiB2
interface became slightly wider due to Au mass transfer.
Our investigations of I−V curves of the Au–TiBx–
Ni–n-21R-SiC contacts taken before and after RTA
showed that the initial samples demonstrated barrier-
type I−V curves [2], while those after RTA had ohmic-
type I−V curves (with ρс≤10-3 Ohm⋅cm2).
The mechanism of ohmic contact formation at
RTA, as well as the properties of the interface between
Ni (and its silicide phases) and SiC, were studied for
specially made test structures.
B. Characterization of Ni(Ni2Si)–n-21R-SiC interface
and ohmic contact
Our studies of I−V curves of the initial Ni–n-21R-SiC
contact structures showed that the I−V curves were of the
barrier type. However, the Schottky barrier height Bϕ
was lower than that in contacts formed with Ni by 0.2 to
0.3 V. This fact indicates that (i) the initial contact
structures involved nickel silicide phases whose work
function is less than that of nickel (see [3]), and (ii) due
to magnetron sputtering of nickel, the SiC substrate was
heated up to temperatures (~250…300 °С) at which
silicide phases are produced (though it was not heated
specially).
The above results agree with those obtained with
XRD – see Fig. 2, curve 1 for the (0001) face. One can
see from Fig. 2 that, even in the initial contact structure,
the phases NiSi, δ-Ni2Si and NiSi2 are present, along
with pure Ni. A comparison between the component
concentration depth profiles in the initial contacts
(Fig. 3a) and phase composition of the contact-forming
layer shows that an extended region is formed in the
Ni−n-21R-SiC contact on the (0001) face. This fact
indicates formation of Ni−Si chemical bonds due to
substrate heating up (even at the metal adsorption stage).
It is in agreement with the data on temperatures of phase
formation for various nickel silicides [4], as well as
correlates with the XRD results obtained for the same
samples.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 67-70.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
69
- -Ni Sid - NiSi- Ni 22- NiSi
35 55 75 9515
SiC SiC
а )
б )
Fig. 2. XRD pattern for Ni–n-21R-SiC samples before (a) and
after RTA (b) at 1000 °С .
RTA of the test structures at Т = 1000 °C leads to
formation of ohmic contacts with the reduced
(≤10–3 Ohm⋅cm2) contact resistivity ρс. It follows from
the XRD data (Fig. 2, curve 2) that, due to RTA,
practically total (not bonded chemically) nickel has
interacted with SiC. In this case, the δ-Ni2Si phase was
formed whose fraction increased as compared to that in
the initial sample. The above results are also supported
by the results on the Auger concentration depth profiles
of contact components after RTA (Fig. 3b), which
indicates at intense silicide formation over the total
metal layer thickness. Repeated RTA at Т = 1000 °C did
not lead to considerable changes in both the parameters
and composition of the Ni2Si−SiC interface.
An analysis of I−V curves at small biases was made
for the contact structures after RTA. It showed that the
Schottky barrier height decreased considerably and was
0.3…0.32 V (for different samples), the ideality factor
being ~1.38…1.4. This indicates the thermionic
mechanism for current flow in contact. In this case,
according to the thermionic emission model, the reduced
contact resistance can be calculated from the following
expression:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
kT
q
TqA
k B
c
ϕ
ρ exp
*
,
0,5 1,0 1,5 2,0
0
20
40
60
80
100
a)
A
t.
%
d/d0
C
O
Ni
Si
0,5 1,0 1,5 2,0
0
20
40
60
80
100
b)
A
t.
%
d/d0
C
O
Ni
Si
Fig. 3. Auger concentration depth profiles of Ni–n-21R-SiC
contact components before (a) and after RTA (b) at 1000 °С .
where k is the Boltzmann constant, q is the electron
charge and *A is the Richardson constant.
At Bϕ ≈ 0.32 V (0.3 V), the cρ value is
~9⋅10–4 Ohm⋅cm2 (~4⋅10–4 Ohm⋅cm2). These results are
in agreement with the typical values [5] for the contact
resistance in the Ni2Si−n-SiC structures, as well as with
our data obtained from direct measurements of ρс.
It should be noted that for some contact structures
after RTA, linear I−V curves were observed, with ρс ≈
≈ 10-3…10-4 Ohm⋅cm2. The distinction in current flow
mechanisms in the Ni2Si–n-21R-SiC contact structures
seems to be due to inhomogeneous phase composition of
metallization. This conclusion is supported by the XRD
results for these samples (see Fig. 2).
C. Thermometric characteristics of the thermistor made
on the basis of n-21R-SiC
The size of SiC thermistor chips produced was 0.5 mm
square by 0.4 mm thick. They were packaged in
cylindrical canister packages, 3 mm in diameter and
5 mm long.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 4. P. 67-70.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
70
Fig. 4. Typical resistance (R), sensitivity (S) and dimensionless
sensitivity (DS) versus temperature curves for n-21R-SiC-bulk
resistance thermometers.
Fig. 4 shows typical thermometric characteristics of
the Au–TiBx–Ni2Si–n-21R-SiC thermistors, namely, the
temperature dependence of resistance R, temperature
sensitivity S = dR/dT, and dimensionless sensitivity, Sd =
= (T/R)(dR/dT), over the temperature range from ~77 up
to 450 K. The thermistor shows very high sensitivity,
changing resistance by 105 times (from 106 down to
10 Ohm) in the temperature range from 77 up to 450 K.
Further investigations are aimed at widening the
operating temperature range of the Au–TiBx–Ni2Si–n-
21R-SiC thermistors to both low and high temperatures.
4. Conclusion
Our investigations have shown that the Au–TiBx–Ni2Si
multilayer contact system is promising for the
production of SiC resistance thermometers having
improved reliability when operating for extended periods
at elevated temperatures. The thermistor developed on
the basis of Au–TiBx–Ni2Si–n-21R-SiC structures is
very promising for highly sensitive temperature
measurements in the 77 to 450 К temperature range.
References
1. O.A. Agueev, The technological problems of
contacts to silicon carbide, TRTU Publishers,
Taganrog, 2005 (in Russian).
2. S.P. Avdeev, O.A. Agueev, R.V. Konakova,
Ya.Ya. Kudryk, O.S. Lytvyn, V.V. Milenin,
D.A. Sechenov, A.M. Svetlichnyi, Modification of
the parameters of metal–silicon carbide contacts
using pulsed thermal treatment // Fizika i khimiya
obrabotki materialov No 6, p. 84-88, 2004 (in
Russian).
3. V.S. Fomenko, Emission properties of materials
(Handbook). Naukova Dumka, Kiev, 1981 (in
Russian).
4. S.P. Murarka, Silicides for VLSI Application.
Academic Press, New York−London, 1983.
5. F. Roccaforte, Processes for SiC devices: new trends
in metallization, in 5th European Conf. on Silicon
Carbide and Related Materials (ECSCRM 2004)
Tutorial, v.1, Bologna, Italia.
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