17
Original scientific paper
Journal of Microelectronics, 
Electronic Components and Materials
Vol. 54, No. 1(2024), 17 – 24
https://doi.org/10.33180/InfMIDEM2024.102
How to cite:
B. Repič et al., “The Effect of Firing Conditions on the Characteristics of Thick-film Resistors for Temperature Sensors", Inf. Midem-J. Micro-
electron. Electron. Compon. Mater., Vol. 54, No. 1(2024), pp. 17–24
The Effect of Firing Conditions on the 
Characteristics of Thick-film Resistors for 
T emperature Sensors
Barbara Repič
1,2
, Darko Belavič
1
, Danjela Kuscer
1,2
1
Electronic Ceramics Department, Jožef Stefan Institute, Ljubljana, Slovenia
2
Jožef Stefan International Postgraduate School, Ljubljana, Slovenia
Abstract: An integrated miniature electrochemical sensor (ES) that offers rapid, sensitive, and selective detection of chemical and 
biological contaminants in a variety of samples requires temperature control to work accurately. To address this, one approach is to 
locate temperature sensor (TS) next to the ES components. However, this integration poses a challenge as different firing processes 
are required for the sensor components and the TS. Commercially available thick-film materials for the realisation of TS are designed 
for screen printing on alumina and firing in air at 850 °C for 10 minutes. However, a key component of an ES, a carbon-based working 
electrode, must be fired in an oxygen-lean atmosphere. In this study, we investigated the influence of the firing atmosphere, i.e., air 
and argon, on the characteristics of thick-film resistors, including thickness, roughness, phase composition, resistivity, and temperature 
dependence. For the study, we used two commercially available thick-film pastes, NTC2114 and NTC2113, as TS with nominal sheet 
resistivities of 10 kΩ/sq and 1 kΩ/sq at 25 °C, respectively. Using X-ray powder diffraction analyses, we detected RuO
2
 and spinel phases 
in the samples heated at 850 °C in air. However, when the samples were fired in argon, we detect metallic ruthenium and alloys. As 
a result of these changes, the resistivity of the NTC2114 and NTC2113 increased significantly. However, despite these changes, the 
relative resistance and the coefficient of temperature sensitivity did not vary significantly, indicating the suitability of these materials 
as TS. These findings have important implications for the future integration of TS into various screen-printed ES systems, fostering the 
design and development of systems with enhanced accuracy and reliability in temperature measurements.
Keywords: NTC, thick film, screen printing, temperature sensors, phase composition
Vpliv pogojev žganja na lastnosti debeloplastnih 
uporov za temperaturne
Izvleček: Miniaturni integrirani elektrokemijski senzorji omogočajo hitro, občutljivo in selektivno zaznavanje kemijskih in bioloških 
onesnaževalcev v različnih vzorcih. Za pridobivanje zanesljivih in natančnih meritev pa je potrebno meriti in/ali kontrolirati 
temperaturo vzorca na samem mestu meritve. Najbolj primerna rešitev je integracija debeloplastnega senzorja temperature v 
elektrokemijski senzorski sistem. Integracija predstavlja izziv, saj so materiali za izdelavo senzorskih komponent in temperaturnega 
senzorja drugačni in zato zahtevajo različne postopke žganja. Komercialni debeloplastni materiali za izdelavo temperaturnega senzorja 
so razviti za sitotisk na inertno podlago iz aluminijevega oksida in za žganje pri temperaturi 850 °C na zraku. Ključna komponenta 
elektrokemijskega senzorja je delovna elektroda na osnovi ogljikovih materialov, ki zahteva žganje pri povišani temperaturi v atmosferi 
z nizko vsebnostjo kisika. V tej študiji smo proučevali vpliv atmosfere žganja debeloplastnih materialov, zrak in argon, na debelino, 
hrapavost, fazno sestavo, upornost in temperaturno odvisnost upornosti. Za študijo smo uporabili paste primerne za sitotisk NTC2114 z 
nazivno plastno upornostjo 10 kΩ/sq in NTC2113 z nazivno plastno upornostjo 1 kΩ/sq. Rezultati so pokazali, da je po žganju na zraku 
v plasteh prisoten RuO
2
 in spinelna faza. V plasteh, žganih pri 850 °C v argonu, teh faz nismo zasledili, pač pa smo detektirali kovinski Ru 
in zlitine. Posledično se je upornost plasti NTC2114 in NTC2113 močno povečala: za faktor 5 pri NTC2114 in za faktor 19 pri NTC2113. 
Kljub tem spremembam pa se relativna upornost in koeficient temperaturne občutljivosti (β) vzorcev nista bistveno premenila, kar 
kaže na primernost teh materialov za izdelavo temperaturnih senzorjev. Te ugotovitve imajo pomembno vlogo za načrtovanje in razvoj 
integracije temperaturnih senzorjev v druge tipe elektrokemičnih sistemov. Prispevale bodo k razvoju takih sistemov, ki omogočajo 
bolj natančne in zanesljive meritve temperature.
Ključne besede: NTC, debele plasti, sitotisk, temperaturni senzor, fazna sestava
* Corresponding Author’s e-mail: danjela.kuscer@ijs.si

18
B. Repič et al.; Informacije Midem, Vol. 54, No. 1(2024), 17 – 24
1 Introduction
Electrochemical sensors are a powerful tool for the rap-
id, sensitive, and selective detection of different types 
of substances in a variety of samples. They are capable 
of detecting chemicals such as heavy metals, pesti-
cides, antibiotics, and food additives as well as biologi-
cal contaminants such as bacteria, viruses, fungi, and 
associated toxins in food, air, water, and soil. As a result, 
these sensors are used in various areas, e.g., for food 
quality control, monitoring environmental conditions, 
and promoting industrial safety [1,2].
The electrochemical detection methods involve the 
interaction between the target compound, i.e., the 
analyte, and the sensor surface, which leads to a redox 
reaction. This reaction produces a detectable signal, 
such as a change in current, potential or impedance, 
which is then measured and related to the qualitative 
and quantitative amount of the analyte. Temperature 
has a major influence on electrochemical measure-
ments. It is therefore important to measure and control 
the temperature when carrying out electrochemical 
measurements [3]. The conventional measurement is 
performed in an electrochemical cell consisting of a 
working electrode (WE), a counter electrode (CE), and 
a reference electrode (RE) immersed in an analyte and 
connected to a potentiostat that controls the electro-
chemical potential and measures the resulting signals. 
However, due to technological advances these three 
electrodes can be integrated onto one substrate, which 
has led to the development of miniaturised, low-cost 
and portable electrochemical sensors (ES). They of-
fer a practical solution for the detection of different 
classes of compounds, especially for non-professional 
users in remote locations, and are suitable for real-time 
sensing applications. One of the most commonly used 
integrated ES is the planar configuration, also known 
as screen-printed electrode (SPE). The name is derived 
from its manufacturing process in which thick-film 
materials, i.e., pastes, are deposited onto a ceramic 
substrate through screen-printing technology. This ap-
proach enables the production of functional, efficient 
and cost-effective ES with good performance charac-
teristics [4,5].
In conventional thick-film technology, thick-film ma-
terials are applied to alumina in paste form using the 
screen-printing process. These deposited thick films 
are dried separately at a temperature of 150 °C and 
then fired at a peak temperature of between 800 °C and 
900 °C in an air atmosphere. For the integrated ES, the 
processing must be adapted to the materials used for 
the electrodes. The RE and CE are usually made of met-
als such as platinum and silver, which can withstand 
these processing conditions. However, the WE is often 
made of carbon-based materials that require a differ-
ent treatment. Carbon-based materials in particular 
need to be fired in an inert atmosphere. This requires 
the investigation of technological processes and the 
verification of technical properties to ensure a compat-
ible process [6].
Since the electrochemical measurements, and thus 
the accuracy and reliability of ES, are strongly depend-
ent on the temperature, it is of utmost importance to 
measure the temperature in the immediate vicinity of 
the WE where the redox reactions take place. This can 
be achieved by integrating an additional electronic 
component, i.e., a temperature sensor (TS), on the alu-
mina substrate next to the electrodes. It is most appro-
priate if the TS is processed with a similar technology as 
the other sensor components, namely by screen print-
ing and subsequent firing. The operating principle of 
the TS is based on the temperature-dependent resistiv-
ity of the thick-film material, which can have a negative 
temperature coefficient (NTC) or positive temperature 
coefficient (PTC) of the resistivity [7–11].
The resistance (R) of thick-film resistors are defined by 
their sheet resistance (R
SH
), their length (l) and their 
width (w), whereby the R
SH
 depends on the resistivity 
(ρ) and the thickness (t) of the screen-printed and fired 
layer. All these relationships are shown in the Eq. (1).
ρ                
SH SH
ll
RR RR
tw tw

  

 (1)
Commercially available thick-film resistors usually con-
sist of ruthenium oxide and/or bismuth ruthenate, and 
have a R
SH
 in decade values from 1 Ω/sq to 10 MΩ/sq. 
Therefore, by using materials with different R
SH
 and a 
different geometry of thick-film resistors, all desired 
different resistances can be achieved. The temperature 
coefficient of resistance (TCR) is described by Eq. (2), 
where R
1
 is the resistance at temperature T
1
 (usually T
1
 
is equal to 25 °C), and R
2
 at T
2
. The TCR values are below 
100×10
−6
 K
-1
 for most resistors [7].

21 21
1 RR TCRT T   

   (2)
Specially designed thick-film resistor materials can be 
used as TS. These materials are designed with a high-
temperature dependence of resistivity. There are sev-
eral commercially available thick-film resistor materials 
with high PTC or NTC of the resistivity [12,13]. Most PTC 
resistors have a linear characteristic of resistivity as a 
function of temperature (Eq. (2)), while most NTC resis-
tors have an exponential characteristic of resistance as 
a function of temperature (Eq. (3)), where β is the coef-
ficient of temperature sensitivity.

19
12
11
21
TT
RR e






    (3)
Commercially available PTC thick-film resistors have a 
R
SH
 between 10 Ω/sq and 1000 Ω/sq, and values of TCR 
between 1000×10
−6
 K
-1
 and 3000×10
−6
 K
-1
. Commer-
cially available NTC thick-film resistors have a R
SH
 be-
tween 1 kΩ/sq and 100 kΩ/sq, and values of β between 
-2000 K and -4000 K. Therefore, NTC sensors are more 
sensitive, especially at low temperatures [8]. Since in 
our work we investigate a relatively low and narrow 
temperature range up to 100 °C and a target resistance 
between 1 kΩ and 10 kΩ, we decided to use NTC thick-
film resistors for the fabrication of TS. The NTC materi-
als are based on the Mn-Ni-Co-O spinel phase with the 
addition of RuO
2
 [10]. NTC pastes have been used for 
the realisation of temperature sensors on alumina and 
low temperature co-fired ceramic (LTCC) [14,15] and in 
microfluidic bioreactors made by multilayer LTCC tech-
nology [16].
NTC resistor has to be processed by similar technol-
ogy as other sensor’s components. NTC screen-printed 
pastes are commercially available and involve firing at 
a temperature of 850 °C in air atmosphere. However, 
the ES component, i.e., the carbon-based working elec-
trode, requires firing in an oxygen-lean atmosphere. 
From our knowledge, no data is available on the pro-
cessing of NTC’s screen-printing pastes in such atmos-
pheres. For compatibility purposes, the processing of 
NTC thick-film resistors in an oxygen-lean atmosphere 
needs to be studied. 
In this work, we designed and processed an integrated 
TS using two commercially available NTC materials. The 
NTC pastes were screen-printed onto alumina substrate 
and fired at 850 °C at different conditions, namely in 
air for 10 min and 30 min, and in argon for 30 min. The 
study relates the firing conditions, thickness and phase 
composition of the thick-film structures to the perfor-
mances of integrated sensors on an alumina substrate. 
The paper presents fabrication and characterization of 
the temperature sensors, highlighting their suitability 
for integration with screen-printed electrodes for elec-
trochemical characterisation.
2 Materials and methods
2.1 Preparation of thick-film samples
Two thick-film thermistor pastes NTC2114 and NTC2113 
(Ferro, King of Prussia, PA, USA) with a nominal R
SH
 of 
10 kΩ/sq and 1 kΩ/sq, respectively, were used for pro -
cessing temperature sensors. Thick-film resistor mate-
rial (2041, DuPont Wilmington, DE, USA) with a R
SH
 of 10 
kΩ/sq was used as the reference thick-film component. 
It was selected because it is considered to be relatively 
insensitive to fluctuations in the production process 
and enables the production of a stable and high-quality 
thick-film resistor [7]. The electrical interconnections and 
contact pads were made from a silver-based thick-film 
conductor (9912MM, ESL, King of Prussia, PA, USA).
The materials were screen printed on an alumina sub-
strate (Rubalit 708S, 96% Al
2
O
3
, CeramTec, Plochingen, 
Germany) with the dimensions 24.0 mm × 10.0 mm × 
0.5 mm using a screen printer (C1010, Aurel, Modigli-
ana, Italy).
The thick-film resistors were deposited on an alumina 
substrate in the form of a square with dimensions of 
8.0 mm x 8.0 mm for the structural investigation and of 
1.1 mm x 1.1 mm with corresponding electrical inter-
connections for the electrical characterisations. Figure 1 
shows the image of test samples, while the layout of 
the latter sample is shown elsewhere [17]. The screen-
printed layers were dried in a dryer at 120 °C for 15 min-
utes and then fired under three different conditions:
i) 850 °C for 10 minutes in air with a heating and 
cooling rate of 33 °C/min in a chamber furnace 
(PEO603, ATV Technologie, Vaterstetten, Ger-
many). The thick-film samples from pastes 2113, 
2114 and 2041 processed with this profile, are re-
ferred to as 2113-10/air, 2114-10/air and 2041-10/
air, respectively.
ii) 850 °C for 30 minutes in a flow of synthetic air. The 
samples were heated in a tube furnace at 450 °C 
for 1 hour at a heating rate of 2 °C/min and then 
heated at 850 °C for 30 minutes at a heating rate 
B. Repič et al.; Informacije Midem, Vol. 54, No. 1(2024), 17 – 24
Figure 1: The photo of the test samples with dimen-
sions 8.0 mm x 8.0 mm (above) and 1.1. mm x 1.1 mm 
(below), where R stands for resistor, EI for electrical in-
terconnection, CP for contact pad, and AO for alumina 
substrate.

20
of 5 °C/min. The samples were cooled to room 
temperature at a cooling rate of 5 °C/min. The 
thick-film samples from pastes 2113, 2114 and 
2041 processed according to this profile, are de-
noted 2113-30/air, 2114-30/air and 2041-30/air.
iii) 850 °C for 30 minutes in a flow of argon. The sam-
ples were heated in a tube furnace at 450 °C for 1 
hour at a heating rate of 2 °C/min and then heated 
at 850 °C for 30 minutes at a heating rate of 5 °C/min. 
The samples were cooled to room temperature at 
a cooling rate of 5 °C/min. The thick-film samples 
from pastes 2113, 2114 and 2041 that were pro-
cessed with this profile, are designated 2113-30/
Ar, 2114-30/Ar and 2041-30/Ar.
2.2 Characterisation
Test samples with dimensions 8.0 mm x 8.0 mm, fired 
for 30 min in air and Ar, were analysed in terms of thick-
ness and phase composition. The thickness of the sam-
ples was measured by a contact stylus profilometer 
(Bruker DektakXT Advanced System, Karlsruhe, Ger-
many). The X-ray powder diffraction (XRD) patterns of 
the samples were collected with a benchtop Powder X-
Ray Diffractometer (MiniFlex 600-C, Rigaku). Diffraction 
patterns were collected at room temperature in the 2θ 
range from 20° to 70° with a step of 0.02°and 0.24 s/step. 
The phases were identified using X’Pert HighScore Plus 
2.1 (PANalytical) and the PDF-4 database (release 2019).
The NTC thick films and resistors with dimensions 
1.1 mm x 1.1 mm, fired in air for 10 min and 30 min, 
and in Ar for 30 min, were characterized in an environ-
mental chamber (VCL 7006, Voetsch Industrietechnik, 
Balingen-Frommern, Germany) at a constant relative 
humidity of about 40 % in the temperature range from 
-25 °C to 125 °C. The resistance of sensors and resistors 
was measured by a multimeter with multiplexed chan-
nels (2700, Keithley Instruments, Cleveland, Ohio, USA). 
The testing and measuring system was computer con-
trolled including the acquisition of data. Resistances at 
25 °C and calculated β, as key characteristics of temper-
ature sensors, were evaluated for all samples.
3 Results and discussion
All thick-film samples fired in air and Ar for 30 min, 
measuring 8.0 mm x 8.0 mm, were about 30 µm thick 
and had a surface roughness R
q
 of 1 µm, regardless of 
the type of material and firing conditions.
XRD analysis of these samples (revealed that the sam-
ples have a high background characterised by an amor-
phous (glassy) phase. The amount of the glassy phase 
is highest in the thick film processed from 2114 paste, 
and lowest in 2041, regardless of the firing atmosphere. 
The background of the samples fired in air and argon is 
similar, indicating that the amount of amorphous phase 
for the selected sample does not vary significantly with 
the firing atmosphere (Figure 2, Figure 3 and Figure 4).
Figure 2: XRD patterns of a) 2113-30/air, and b) 2113-
30/Ar. : Ni-Mn-Co-O, : alloys, : RuO
2
, : Ru, : 
Al
2
O
3
, : cubic SiO
2
 and : orthorhombic SiO
2
.
B. Repič et al.; Informacije Midem, Vol. 54, No. 1(2024), 17 – 24
Figure 3: XRD patterns of a) 2114-30/air, and b) 2114-
30/Ar. : Ni-Mn-Co-O, : alloys, : RuO
2
, : Ru, : 
Al
2
O
3
, : cubic SiO
2
 and : orthorhombic SiO
2
.
The phase composition of the 2113-30/air and 2114-30/
air is similar. In all the patterns we identify Ni-Mn-Co-O 
spinel phase (PDF 01-084-8364), RuO
2
 (PDF 01-075-
4303), alumina (PDF 01-075-6775) and cubic SiO
2
 (PDF 
01-080-4050). An additional peak at ∼34 degrees is ob-

21
served in 2114-30/air, characterised by orthorhombic 
SiO
2
 (PDF 04-012-8095). The phase composition of the 
2041-30/air is different than those of 2113-30/air and 
2114-30/air. In the pattern we identify RuO
2
 (PDF 01-
075-4303), Bi
2
Ru
2
O
7
 (PDF 04-013-7147), alumina (PDF 
01-74-6775), hexagonal SiO
2
 (PDF 01-078-1257) and 
PbO
2
 (PDF 04-020-6664). The phase composition of the 
air-fired samples corresponds well to the composition, 
reported for NTC materials and resistors [7,13].
The samples fired in argon atmosphere have very dif-
ferent phase composition compared to air-fired sam-
ples. In the pattern of 2113-30/Ar and 2114-30/Ar we 
have not identified any spinel phase, but metallic Ru 
(PDF 01-071-3766), and a phase that could correspond 
to alloys, such as Mn-Ni (PDF 04-003-2244) and Ni-Ru 
(PDF 03-065-4309), Co-Mn-O rock-salt structure (PDF 
04-021-8068), alumina (PDF 01-75-6775), orthorhom-
bic SiO
2
 (PDF 04-012-8095), Mn
2
SiO
4
 (PDF 00-009-0485) 
and Ni
2
SiO
4
 (PDF 04-014-7800). Although partial de-
composition of Mn-Ni-O spinel upon heating at el-
evated temperature in air has been reported [19], our 
results showed that the spinel phase decomposed 
completely when the sample was heated to 850 °C in 
an argon atmosphere. The shift of diffraction peaks for 
rock-salt structure observed in 2113-30/Ar and 2114-
30/Ar indicates, that its chemical composition in the 
two samples is different. In the 2041-30/Ar reference 
sample, we identify the characteristic peaks for Ru (PDF 
01-071-3766), Pb
2
O (PDF 00-002-0790), PbO
2
 (PDF 04-
020-6664), Bi
2
O
3
 (PDF 01-079-6675), as well as alumina 
(PDF 01-075-6775) and cubic SiO
2
 (PDF 01-080-4050). 
These results clearly indicate that the spinel phase and 
RuO
2
 decompose to metals and/or alloys when the 
thick-film resistors are fired in an argon at 850 °C. We 
expect that the resistivity of the argon-fired thick films 
will be very much different compared to air-fired sam-
ples, since the amount of RuO
2 
and spinel phase dictate 
the resistivity of the NTC resistors [13,15–17].
Figure 5, Figure 6 and Figure 7 show the temperature 
dependences of the resistances and relative resistances 
for NTC2113, NTC2114 and 2041 after firing at 850 °C at 
B. Repič et al.; Informacije Midem, Vol. 54, No. 1(2024), 17 – 24
Figure 5: Resistances (a) and relative resistances (b) as 
a function of temperature for 2113-10/air ( ), 2113-30/
air ( ), 2113-30/Ar ( ).
Figure 4: XRD patterns of a) 2041-30/air, and b) 2041-
30/Ar. #: Bi
2
Ru
2
O
7
, : Bi
2
O
3
, : RuO
2
, : Ru, : PbO
2
, : 
Pb
2
O, : Al
2
O
3
, : cubic SiO
2
 and : hexagonal SiO
2.
Figure 6: Resistances (a) and relative resistances (b) as 
a function of temperature for 2114-10/air ( ), 2114-30/
air ( ), 2114-30/Ar ( ).

22
different conditions. The firing of the samples in air for 
10 min and 30 min resulted in similar resistances while 
firing in an argon significantly increases the resistance 
of all the samples. The R
SH
 of NTC2114 and NTC2113 
increased by a factor of 5 and 19, respectively, while 
for the resistor 2041 it increased by a factor of 3. These 
changes in R
SH
 can be attributed to the absence of RuO
2
 
and spinel phase. However, despite these changes, the 
relative resistance and the coefficient of temperature 
sensitivity (β) did not vary significantly. The tempera-
ture range of the electrochemical sensor operation lies 
between 10 °C and 70 °C. In this temperature range, 
the maximum resistance value is around 100 kΩ for the 
NTC2114 and around 60 kΩ for the NTC2113.
minutes increases the β by about 5 % in air and about 
7 % in argon. The longer firing time of the NTC2113 in-
creases the β by about 10 % and about 22 % when fired 
in air and argon, respectively. The thick-film resistor ma-
terial 2041, which is used as a reference material, show 
a resistivity-independent temperature dependence. 
The air and Ar-fired NTC thick films have similar values 
of relative resistance and β, which makes them suitable 
for use as temperature sensors. However, when consid-
ering temperature-dependent resistivity and R
SH
, the 
NTC2113 is a more appropriate material for processing 
temperature sensor, particularly due to easier signal 
conditioning.
4 Conclusions
A miniature electrochemical sensor (EC) needs temper-
ature control for accurate operation, and one possible 
approach is to position temperature sensors near the 
EC. The EC component, the C-based working electrode, 
requires firing in an oxygen-lean environment, while 
temperature sensors are fired in air. In this study, we ex-
plored the processing of commercially available thick-
film resistors, NTC2113, NTC2114, and resistor 2041, 
deposited on alumina substrates using screen-printing 
method and firing at 850 °C in air for 10 and 30 min and 
argon for 30 min. Obtained thick films were 30 μm thick 
with 1 μm surface roughness, regardless of the firing 
conditions, confirmed by profilometry. X-ray powder 
diffraction analysis showed that the films contained 
an amorphous phase, and its quantity did not vary sig-
nificantly in air and argon for the selected samples. NTC 
thick films fired in air contained RuO
2
, Ni-Mn-Co-O spinel 
phase, and minor phases, alumina, and SiO
2
. The refer-
ence resistor contained RuO
2
 and bismuth ruthenate as 
major phases, together with lead oxide, alumina, and 
SiO
2
. We found out that argon-fired samples did not 
Figure 7: Resistances (a) and relative resistances (b) as 
a function of temperature for 2041-10/air ( ), 2041-30/
air ( ), 2041-30/Ar ( ).
B. Repič et al.; Informacije Midem, Vol. 54, No. 1(2024), 17 – 24
Table 1 shows R
SH
 values measured at 25 °C, and β val-
ues calculated in the temperature range between 0 °C 
and 75 °C of the NTC2113, NTC2114 and 2041 resistors 
fired at different firing conditions.
The longer firing time in air has no significant influence 
on the R
SH
. For samples fired for 10 and 30 minutes in 
air it varied for approximately +18 %, -17 %and -2 % for 
NTC2113, NTC2114 and 2041, respectively. On the oth-
er hand, firing in argon has a significant effect on R
SH
. 
Compared to conventional firing in air for 10 minutes, 
the R
SH
 increased by factors of 19, 5 and 3 for NTC2113, 
NTC2114 and 2041, respectively.
The temperature dependence of the thick-film materi-
als, expressed by the β, is relatively insensitive to the 
firing conditions. Compared to conventional firing con-
ditions, 850 °C for 10 min in air, firing NTC2114 for 30 
Table 1: Sheet resistivity (R
SH
) at 25 °C and coefficients 
of temperature sensitivity (β) in the temperature range 
between 0 °C and 75 °C of NTC2113, NTC2114 and 2041 
fired at different firing conditions.
Sample
R
SH
 at 25 °C  
[Ω/sq]
β calculated at 
0/75 °C [K]
2113-10/air
2113-30/air
2113-30/Ar
2130
2522
40937
-1840
-2019
-2250
2114-10/air
2114-30/air
2114-30/Ar
13008
10822
64507
-2317
-2441
-2480
2041-10/air
2041-30/air
2041-30/Ar
10269
10014
34394
1
16
-7

23
exhibit RuO
2
, spinel phase, or bismuth ruthenate, but 
rather metallic ruthenium and alloys. Consequently, 
the resistivity of the argon-fired samples was signifi-
cantly higher compared to the air-fired samples. For 
materials fired in argon, the R
SH
 increased by a factor 
of 19 and 5 for NTC2113 and NTC2114, respectively. 
Additionally, the R
SH
 of the reference resistor increased 
by a factor of 3. The relative resistances and β for NTC 
materials were relatively unaffected by the firing atmo-
sphere. Therefore, NTC materials show potential for use 
as temperature sensors. Among them, NTC2113, with 
its lower R
SH
, is a more suitable material due to easier 
signal conditioning.
5 Acknowledgement
This work was supported by the Slovenian Research 
and Innovation Agency, grant numbers P2-0105, J2-
3049 and PR-11483. 
We thank Ivana Goričan for recording X-ray powder dif-
fraction patterns and Mitja Jerlah for screen-printing of 
selected test samples.
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Arrived: 26. 01. 2024
Accepted: 26. 02. 2024
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