Thick-film Thermistors Research Articles

‘Lead Free’ thick film thermistors: a study of variation in glass frit concentration and organics composition

There is a need to develop environment friendly electronic materials due to worldwide constraint for the use of hazardous chemicals such as lead, cadmium which are the main constituents of the electronic components. Considering such need, the work on lead free thick film thermistors has been initiated. Thick film materials have been proved to possess economical processing and functional advantage over other technologies and quick turnaround production of hybrid microcircuits. Thick film thermistors are different from the conventional thermistors (bulk) not only by the preparation process but also in composition, transport properties etc. In this paper, we have specifically focused on the influence of glass frit content and organic composition on the properties of lead free spinel based NTC thermistors. We noted that the glass frit concentration is responsible for the change in physical as well as electrical properties of the thick film thermistor. However, the type of organic vehicle (i.e., composition) did not show any adverse effect on microstructure and electrical properties of the thermistor.

Thick-film NTC thermistors and LTCC materials: The dependence of the electrical and microstructural characteristics on the firing temperature

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film NTC thermistors (4993, EMCA Remex) fired either on LTCC (low-temperature cofired ceramic) substrates or buried within LTCC structures were evaluated. The thermistors were fired at different temperatures to study the influence of firing temperature on the electrical characteristics. The results were compared with the characteristics obtained on alumina substrates. The sheet resistivities were higher than the resistivities of thick-film thermistors on alumina substrates. The increase of the sheet resistivities was attributed to the diffusion of the glass phase from the rather glassy LTCC substrates into the NTC thermistors. This was confirmed by EDS analyses. However, the increase in the resistivity was linked to an increase of the beta factors. Therefore, the results show that the evaluated NTC thermistors on LTCC substrates can be used for temperature sensors in MCM-Cs as well as in MEMS LTCC structures. When the thermistors were buried in the LTCC substrates, the LTCC structures delaminated during firing, leading to high sheet resistivities and high noise indices. This delamination is attributed to the different sintering rates of the NTC and LTCC materials.

Low temperature synthesis and characterization of NTC powder and its ‘lead free’ thick film thermistors

A general and simple chemical approach has been proposed to prepare negative temperature coefficient (NTC) powder material using commercially available tetra hydrated acetates of Mn, Co, Ni and oxalic acid. The thermal decomposition of Mn-Co-Ni oxalate at 700^oC leads to formation of spinel phases with fine powder material. Lead free thick film thermistor pastes were formulated using the synthesized spinel powders. Planar thick film thermistor patterns of the formulated pastes were screen printed on alumina substrates. The microstructure and electrical properties of these thick film thermistors were determined. Depending on the powder preparation, the prepared thick film NTC thermistors showed room temperature resistance in the range of [email protected] The values of thermistor constant, @b25/300 ranged from 4014 to 4223K.

EM Simulator Analysis of Optimal Performance Thick-Film Segmented Thermistors versus Material Characteristics Selection

In this paper, an alternative approach to the analysis of thick-film segmented negative temperature coefficient thermistors based on the use of a commercial electromagnetic simulator tool is presented. The influence of the geometrical parameters and material characteristics of the used thermistor paste on the overall thermistor performance was analyzed and simulated. A physical model for the segmented thermistors is given in brief, together with experimental data. The diffusion of electrode metal into the thermistor layer was analyzed, simulated, and estimated. Obtained simulation results were compared with experimental results, and the validity of the adopted approach was verified.

Properties of thick film Ni 0.6Co 0.4Fe yMn 2− yO 4: (0 ≤ y ≤ 0.5) NTC ceramic

Fritless thick film of NTC thermistors were prepared by screen printing Ni 0.6Co 0.4Fe y Mn 2− y O 4: (0 ≤ y ≤ 0.5) ceramic, synthesized by oxalate co-precipitation method on alumina. The composition dependent resistivities, thermistor constant were investigated for the bulk (pellet form) and thick film ceramic. Fritless thick film thermistors have room temperature resistivities only four to five times that of corresponding bulk ceramic. Both the thick film and bulk Ni 0.6Co 0.4Fe yMn 2− y O 4: (0 ≤ y ≤ 0.5) ceramic comply with Arrhenius equation. Ni 0.6Co 0.4Fe 0.2Mn 1.8O 4 shows least room temperature resistivity and high thermistor constant. Screen printed NTC thick film thermistors Ni 0.6Co 0.4Fe y Mn 2− y O 4: (0 ≤ y ≤ 0.5) with inorganic binder can be a low cost, reliable temperature sensor in planar form.

Electrical properties of thick-film NTC thermistor composed of Ni 0.8Co 0.2Mn 2O 4 ceramic: Effect of inorganic oxide binder

The thick-film NTC thermistors were prepared by screen printing Ni 0.8Co 0.2Mn 2O 4 ceramic on the alumina. The influence of inorganic oxide binder composition and thickness of thermistor layer on the thermistor constant and initial resistivity are studied. The relation between the resistivity ( ρ) and the absolute temperature for the prepared thick-film thermistor comply with Arrhenius equation. The room temperature sheet resistivities of the thick films were in the range 0.56–7.45 MΩ cm and temperature sensitivity index in the range 1492–3335 K. Binder composition dependent agglomeration of microcrystallites is observed in the microstructure of the thick-film Ni 0.8Co 0.2Mn 2O 4 ceramic. The spinel ceramic was prepared by oxalate co-precipitation and sintering.

Fabrication and characterization of bulk and thick film perovskite NTC thermistors

Purpose – The aim of the present work was the characterization of a group of compounds with the perovskite‐type structure in respect of their applicability as thermistor materials.Design/methodology/approach – Four compositions: La0.7Sr0.3Zr0.5Co0.22+Co0.33+O3, La0.8Sr0.2Ti0.5Co0.32+Co0.23+O3, La0.4Sr0.6Ti0.3Fe0.7O3 and CaTi0.8Co0.2O3 were synthesized by solid‐state reaction. Ceramic thermistor materials were sintered in the temperature range 1,300‐1,400°C. The synthesized powders were used for fabrication of thick film pastes and thermistors fired at 1,100‐1,250°C. Resistance‐temperature characteristics of the ceramic samples were studied in the range −55 to 800°C for the ceramic samples and 20‐600°C for thick films. Endurance tests at 300°C for 500 h were performed.Findings – The developed NTC materials exhibited high temperature coefficients of resistivity, dense microstructure and good stability. The most advantageous characteristics have been shown by La0.7Sr0.3Zr0.5Co0.22+Co0.33+O3 and La0.8Sr0.2Ti0...

Thick film NTC thermistor for wide range of temperature sensing

PurposeAims to focus on temperature sensors.Design/methodology/approachNegative temperature co‐efficient thermistor powders of ternary Mn, Co, Ni oxide along with RuO2 synthesized at relatively moderates temperature (1,000°C). Thick film thermistor paste compositions were formulated by mixing the semiconducting oxide powder, glass frit and organic vehicle. The physico‐chemical analysis, viz. X‐ray diffraction, scanning electron microscopy and thermogravimetry and IR spectroscopy were carried out for the synthesized powder and the resultant thick films. The X‐ray analysis of the powders showed the cubic spinel structure. The electrical properties like thermistor constant, sensitivity index and activation energy of the thick film NTC thermistor were determined.FindingsThe room temperature resistance is observed to range from 490 KΩ to 4.13 MΩ with thermistor constant ranging from 3,275 to 3,980 K, in the temperature range of 25‐300°C.Originality/valueDescribes research work on temperature sensors that are used for monitoring and control in many fields such as in home appliances, manufacturing industries, biomedical and automobile industries.

Modeling and simulation of NTC thick film thermistor geometries

PurposeThe paper aims to focus on thick film planar thermistors.Design/methodology/approachThick film planar thermistors such as rectangular, sandwich, multilayer, segmented and interdigitated were printed of law temperature NTC paste called NTC 3K3 95/2 (Ei Iritel). Their resistivity was measured at room temperature as a function of volume resistivity variations due to electrode effect (diffusion of PdAg into NTC layer) and variation of geometrical parameters such as length l, width w, thickness d, number of segments n. The experimental data obtained were used in forming a model by the simple fitting procedure for counting diffusion effect on volume resistivity and resistivity dependence on geometrical parameters.FindingsThermal behavior of NTC thick films was measured in the range of −30‐120°C. Exponential factor B was fitted for measured values and included in the proposed thick film thermistors model. The agreement of measured and calculated data enables simulation of new thermistor geometries.Originality/valueThe paper focuses on the experiment which was the first step in forming a total physical/mathematical model proposed for thick film thermistor resistivity.

Thick-film PTC thermistors and LTCC structures: The dependence of the electrical and microstructural characteristics on the firing temperature

The electrical and microstructural characteristics of 1 kΩ/sq thick-film thermistors with high positive temperature coefficients of resistivity, i.e., PTC 5093 (Du Pont) fired either on “green” LTCC (low-temperature co-fired ceramics) substrates or buried within LTCC structures, were evaluated. The thermistors were fired at different temperatures to study the influence of firing temperature on the electrical characteristics. The noise indices of the surface resistors fired at temperatures between 850 °C and 950 °C were very low, around −30 dB. The TCRs of the evaluated PTC thermistors were over 3000 × 10 −6/K. The dependence of the resistivity on the temperature between −25 °C and 125 °C was linear, with the values of R 2 being better than 0.9999, regardless of the processing conditions. These results show that PTC thermistors co-fired on LTCC substrates can be used for temperature sensors in MCM-Cs as well as in MEMS structures. However, when the thermistors were buried in the LTCC substrates, the LTCC structures delaminated during firing and blisters formed, leading to high sheet resistivities and high noise indices. This delamination is attributed to the different sintering rates of the PTC and LTCC materials as well as to the expansion of the air bubbles captured in the viscous glass of the PTC material.

The development of the microstructural and electrical characteristics of NTC thick-film thermistors during firing

One kohm/sq. thick-film NTC thermistors (4993, EMCA Remex) with high, non-linear and negative temperature coefficients of resistivity were fired at different temperatures. The development of the resistors’ conductive phase and microstructure was investigated by X-ray diffraction analysis and by scanning electron microscopy. Sheet resistivities, beta factors and noise indices were measured as a function of the firing temperature. In the fired layers of the thermistors the X-ray analyses showed mainly spinel phase and RuO2, which is added to the thick-film NTC materials to decrease the specific resistance and to improve the stability and the current noise. Higher firing temperatures led to more densely sintered microstructures, to increased resistivities and to higher beta factors. The higher resistivities were attributed to the partial exchange of ions on the “B” sites of the spinel structure with aluminium ions.

Development of LTCC Smart Channels for Integrated Chemical, Temperature, and Flow Sensing

This paper describes the development of “smart” channels that can be used simultaneously as a fluid channel and as an integrated chemical, temperature, and flow sensor. The uniqueness of this device lies in the fabrication and processing of low-temperature co-fired ceramic (LTCC) materials that act as the common substrate for both the sensors and the channel itself. Devices developed in this study have employed rolled LTCC tubes, but grooves or other channel shapes can be fabricated depending on the application requirements. The chemical transducer is fabricated by depositing a conductive polymer “ink” across a pair of electrodes that acts as a chemical resistor (chemiresistor) within the rolled LTCC tube. Volatile organic compounds passing through the tube are absorbed into the polymers, causing the polymers to reversibly swell and change in electrical resistance. The change in resistance is calibrated to the chemical concentration. Multiple chemiresistors have been integrated into a single smart channel to provide chemical discrimination through the use of different polymers. A heating element is embedded in the rolled tube to maintain a constant temperature in the vicinity of the chemical sensors. Thick-film thermistor lines are printed to monitor the temperature near the chemical sensor and at upstream locations to monitor the incoming ambient flow. The thermistors and heating element are used together as a thermal anemometer to measure the flow rate through the tube. Configurations using both surface-printed and suspended thermistors have been evaluated.

Composition dependent resistivity of thick film Ni(1−x)CoxMn2O4: (0 ≤ x ≤ 1) NTC thermistors

The fritless thick film NTC thermistor of composition Ni(1−x)CoxMn2O4: (0≤x≤1), synthesized by oxalate co-precipitation, were prepared by screen-printing on alumina substrate. The composition dependent room temperature resistivities, thermistor constant are investigated. The relation between logarithm of resistivity (ρ) and reciprocal of absolute temperature for the prepared thick film thermistor was almost linear for all the compositions studied. The thick film thermistor with ceramic composition Ni0.6Co0.4Mn2O4 was the best with high sensitivity and lowest room temperature resistivity. Highly temperature dependent effects are also observed for temperature below 340 K.

Evaluation of compatibility of thick-film PTC thermistors and LTCC structures

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive temperature coefficients of resistivity, i.e. PTC 5093 (Du Pont) fired either on “green” LTCC (low temperature cofired ceramics) substrates or buried within LTCC structures, were evaluated. The active phase (ruthenium oxide) in the PTC thermistors is not present in the dried films but is formed during firing due to the decomposition of the ruthenate phase. Because of interactions between a glassy LTCC material and thermistors electrical characteristic, i.e. sheet resistivities and noise indices of thermistors fired on the surface LTCC substrates, changed from values obtained on alumina substrates. The differences in the measured electrical parameters were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and Al 2O 3, was confirmed by microanalysis. In the case of buried thermistors, presumably due to the incompatibility of both materials, the structure de-laminated during firing. Cracks between the buried PTC films and the LTCC substrates as well as cracks in PTC films resulted in high sheet resistivities and high noise indices.

Thick-film temperature sensors on alumina and LTCC substrates

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive or negative temperature coefficients of resistivity, i.e., PTC 5093 (Du Pont) and NTC 4993 (EMCA Remex), fired on alumina or co-fired on “green” low-temperature co-fired ceramic (LTCC) substrates, are compared. The active phase in both materials (the ruthenium oxide and the semiconducting spinel in the PTC and NTC thermistors, respectively) is not present in the dried films but is formed during firing. The differences in the measured electrical parameters (sheet resistivities, temperature dependence of resistivities and noise) of the thermistors, fired on alumina or on LTCC were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and SiO 2, was confirmed by microanalysis.

Electrical properties of Ni–Mn–Co–(Fe) oxide thick-film NTC thermistors prepared by screen printing

Ni–Mn–Co–(Fe) oxide thick films were coated on an alumina substrate by a screen-printing technique. The electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. All the thick-film negative temperature coefficient (NTC) thermistors prepared showed a linear relationship between log resistivity and the reciprocal of the absolute temperature, indicative of NTC characteristics. As the amount of Mn3O4 in (Ni2−x Mn x Co1.0)O4 (0.6≤x≤1.8) thermistors increased, the resistivity and the coefficient of temperature sensitivity decreased to a minimum value and then increased again. Also, at a given Ni–Mn oxide content, the resistivity and the coefficient of temperature sensitivity for (Ni1.0Mn1.0Co1−x Fe x )O4 (0.25≤x≤1.0) and (Ni0.75Mn1.25Co1−x Fe x )O4 (0.25≤x≤0.75) thermistors increased with increasing Fe2O3 content. The influence of composition and sintering temperature on the electrical properties of the thermistors is discussed.

Tungsten trioxide-based thick-film NO sensor: design and investigation

New thick-film WO 3 based sensors for the determination of NO levels in steam power plants emissions developed and manufactured at the Laboratory of Electronic Engineering Materials (PTI, Minsk) have been tested in NO, CO or CH 4 containing environments. WO 3(Bi 2O 3) thick films have been used as NO sensitive elements in the sensors. The same metal oxide composition has been successfully applied as the base of built-in thick-film thermistors in the sensors developed. The sensors display high sensitivity to NO in air while remaining unresponsive to common interfering gases such as carbon monoxide or methane. It has been established during preliminary investigations that the sensor operating temperature has to be 300°C, because the ambient temperature varies between 250 and 290°C in boiler shunt tubes where gas sensors are usually set. The characteristics of the sensors have been investigated at 300°C in detail. The results of the investigations are discussed.

Structural, electrical and infrared optical properties of vanadium pentoxide (V2O5) thick-film thermistors

Vanadium pentoxide (V 2 O 5 ) thick-film thermistors have been successfully prepared by screen-printing vanadium trioxide (V 2 O 3 ) and firing in the temperature range 673–873 K. It has been observed by means of X-ray diffraction (XRD) and differential thermal analysis (DTA) that the V 2 O 3 material undergoes transformation to V 2 O 5 during the firing process. The screen-printed resistors have a temperature coefficient of resistance (TCR) varying from −37 000 to −17 000 ppm/K and the thermistor constant ( B ) is 2000 K over the temperature range 200–400 K. Also the resistors have improved morphology, in terms of homogeneous distribution of constituent phases, void content and crystallinity, and hence an increased conductivity as the firing temperature is increased. The resistors have a typical r.m.s. current noise voltage of 10 μV for 40 V bias voltage.

Research on NTC thermally sensitive powder materials for thick-film thermistors

Negative temperature coefficient (NTC) thermally sensitive powder materials made of semiconductor ceramics are crucial for the fabrication of thick-film thermistors. This paper presents several new experimental methods and the results of research on NTC thermally sensitive semiconductor ceramics in the MnCoNi and MnCoNiRu systems. Formulation of the constituents, preparation methods and preparation techniques for the materials are also described.

Influence of Composition and Construction Parameters on the Basic Properties of Thick Film Thermistors

This paper presents experimental data associated with the properties of thick film thermistors based on a spinel‐type semiconducting oxide/RuO2/glass system. The following parameters—sheet resistivity, thermistor (B) and thermal time (?) constants—have been measured, all as functions of different composition and construction variants. The thermistor properties are independent of configuration and are mainly determined by the semiconducting oxide particle chains. The correlation between B and ? for the compositions considered has been observed.