Design and fabrication of a capacitive infrared detector with a floating electrode and thermally isolatable bimorph legs

A new capacitive infrared detector structure that incorporates one electrically floated top electrode that acts as an infrared absorber and two bottom electrodes is proposed and fabricated. The concept begins from an attempt to remove metal lines, the main heat transfer media in the thermal-type infrared detector, from the device's thermal insulation section. A thermal insulation section can be composed without metal lines and instead be solely comprised of an insulator having very low thermal conductivity compared to metals. Therefore, low thermal conductance can be easily achieved with small dimensions of thermal insulation section material. The floating electrode is electrically disconnected from the substrate. Instead, the capacitance change is read only using the two bottom electrodes, which are separated from the absorber and placed on the substrate. The position of the top electrode (infrared absorber) is changed through a bimorph actuation in accordance with the absorption of LWIR (8–12 μm) rays, with an absorptance of 70%. This approach provides an enlarged fill-factor (25%) compared with earlier devices, because the portion of the leg in the pixel area is reduced, whereas the portion of the absorber area is increased. With the small dimension of the thermal insulation section (0.2 × 2 × 10 μm³), thermal conductance of 1.27 × 10⁻⁷ W/K is achieved. In addition, the shortened leg lends the device a higher spring constant relative to the conventional devices, and therefore a higher signal reading voltage can be achieved, resulting in increased temperature responsivity. With the bimorph-type infrared detector's characteristics of low noise and high sensitivity, the proposed structure can achieve a low NETD value of 12.7 mK.     

铌酸锂晶片热释电红外探测器设计及性能测试

通过红外热释电探测器工作原理的分析,采用合适的半导体加工工艺将铌酸锂晶体母材减薄,并对减薄后铌酸锂晶片进行溅射、镀膜将其制成红外敏感单元。选用CMOS放大器与匹配的电阻、电容组成前置放大电路,对热释电信号进行放大和转换;根据红外光谱吸收原理,在敏感单元前封装了窄带滤光片从而提高了敏感单元选择吸收的性能。将敏感单元、前置放大电路和窄带滤波片三部分封装在一个壳体内,红外探测器制作成功。设计了信号调理电路,对从探测器得到的热释电信号进行二次放大和滤波;搭建了探测器响应测试系统,对探测器的性能进行测试,测试验证了该探测器设计的合理性。     

ANSYS在热释电薄膜红外探测器二维热分析中的应用

根据热释电薄膜红外探测器的结构和实际的测试条件,利用有限元软件ANSYS建立了不同结构组成的热释电薄膜红外探测器的二维模型,并对其进行了热分析,得到了探测器内的温度场分布.分析了复合热释电薄膜红外探测器的绝热层对温度场的影响,并将复合热释电薄膜红外探测器与微桥结构探测器的性能进行了比较.     

The study of a novel crystal SiGeC far infrared sensor with thermal isolated by MEMS technology

In this study, we report the design, fabrication and performance of a novel crystal SiGeC infrared sensor with thermal isolation structure. The developed sensor was prepared using the technology of micro-electromechanical systems (MEMS) to achieve a better thermal isolation structure. The operation principle of the sensor is based on the change of thermistor’s resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si_0.68Ge_0.31C_0.01 thin films for its large activation energy 0.21 eV and the temperature coefficient (TCR) of ?2.74%, respectively. Finite element method (FEM) package ANSYS has been employed for the analysis of the thermal isolation and stress distribution in the IR detector. The major FIR-sensing part on the micro-bridge with dimensions of 2,000 × 2,000 × 25 μm³ is fabricated by anisotropic wet etching. Responsivity, thermal conductance, thermal time constant were investigated and found that the thermal isolation improved structure possesses a much superior performance.     

The study of a novel crystal SiGeC far infrared sensor with thermal isolated by MEMS technology

In this study, we report the design, fabrication and performance of a novel crystal SiGeC infrared sensor with thermal isolation structure. The developed sensor was prepared using the technology of micro-electromechanical systems (MEMS) to achieve a better thermal isolation structure. The operation principle of the sensor is based on the change of thermistor’s resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si_0.68Ge_0.31C_0.01 thin films for its large activation energy 0.21 eV and the temperature coefficient (TCR) of −2.74%, respectively. Finite element method (FEM) package ANSYS has been employed for the analysis of the thermal isolation and stress distribution in the IR detector. The major FIR-sensing part on the micro-bridge with dimensions of 2,000 × 2,000 × 25 μm³ is fabricated by anisotropic wet etching. Responsivity, thermal conductance, thermal time constant were investigated and found that the thermal isolation improved structure possesses a much superior performance.

     

High performance human information sensor

High performance human information sensing system, which can monitor the human conditions in a room, especially the number of occupants, their locations and activities, has been developed. The sensor head module of this sensing system consists of a vertical one-dimensional 16-element array detector fabricated by sheet forming method of pyroelectric PbTiO₃ ceramics, an IR-transparent spherical lens, a horizontal scanning mechanical part and a cylindrical mechanical chopping part. The IR lens characteristics have been determined to optimize the sensor output. The sensor is able to detect a two-dimensional thermal distribution (16×60) and the human condition information in a room. The sensor is cost-effective and the sensor head module is small (64 mm in diameter and 79 mm in height) with high resolution. Furthermore, nine times higher resolution with 48×180 thermal distribution was accomplished by the neighbor output averaging scheme. By using this sensing system with high sensitivity and high resolution, the small thermal object such as a lighted cigarette as well as the number of persons in a room can be detected accurately.     

Integrated micro Pirani gauge based hermetical package monitoring for uncooled VO x bolometer FPAs

This paper presents the design and fabrication of a micro Pirani gauge using VO _x as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays (FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO _x thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the measured device TCR is about −0.8% K⁻¹ and the sensitivity about 1.84 × 10⁻³ W K⁻¹ mbar⁻¹.     

Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin

The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ∼23 °C, and the mean skin temperatures averaged ∼35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms⁻¹), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ∼35 °C, the evaporative resistance, R_et, varied between 36 and 60 m² Pa W⁻¹. These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.     

Fabrication and characterization of Pb-free transparent dielectric layer for plasma display panel

Glasses within the Bi₂O₃–B₂O₃–BaO–ZnO system were examined as potential replacements for PbO-based glass frits with low firing temperatures. These frits are used in the transparent dielectric layer of plasma display panels (PDP). The glass transition temperature (T_g) of the prepared glasses varied between 450 and 460 °C. These glasses display dynamic dielectric properties, high transparency and thermal expansion as well as matching well with substrate glass. The thermal coefficient of expansion (TCE) was with the desired range of 81–86×10⁻⁷/K. Moreover, when the screen printed film was heat-treated at 570 °C for 30 min, optical transmittance (83%), root-mean square (rms) roughness (177.6 Å), dielectric constant (10.25) and withstand voltage (4.15 kV) satisfied the requirements necessary for transparent dielectric layers to be used in PDP applications.     

Simple fabrication of an uncooled Al/SiO2 microcantilever IR detector based on bulk micromachining

A simple microfabrication process to make an uncooled aluminum/silicon dioxide bi-material microcantilever infrared (IR) detector using silicon bulk micromachining technology is presented in this work. This detector is based on high banding of the microcantilever due to the large dissimilar in thermal expansion coefficients between the two materials. It consists of a 1 μm SiO₂ layer deposited by 200 nm thin Al layer. Since no sacrificial layer is used in this process, complexity related to releasing sacrificial layer is avoided. Moreover Al is protected in Si etchant using dual-doped tetramethyl ammonium hydroxide. The other advantage of this process is that only three masks are used with four photolithography process. Thermal and thermal mechanical behaviors of this structure are obtained using finite element analysis, and the maximum temperature and displacement at the end of cantilever at 100 pW/μm² absorbed IR power density on top surface are 7.82°K and 1.924 μm, respectively.     

Fabrication of micro sensors on a flexible substrate

Flexible micro temperature and humidity sensors on parylene thin films were designed and fabricated using a micro-electro-mechanical-systems (MEMS) process. Based on the principles of the thermistor and the ability of a polymer to absorb moisture, the sensing device comprised gold wire and polyimide film. The flexible micro sensors were patterned between two pieces of parylene thin film that had been etched using O₂ plasma to open the contact pads. The sacrificial Cr spacer layer was removed from the Cr etchant to release the flexible temperature and humidity sensors from the silicon substrate. Au was used to form the sensing electrode of the sensors while Ti formed the adhesion layer between the parylene and Au. The thickness of the device was 7 ± 1 μm, so the sensors attached easily to highly curved surfaces. The sensitivities of the temperature and humidity sensor were 4.81 × 10⁻³ °C⁻¹ and 0.03 pF/%RH, respectively. This work demonstrates the feasibility and compatibility of thin film sensor applications based on flexible parylene. The sensor can be applied to fuel cells or components that must be compressed.     

The V-Zn binary system: New experimental results and thermodynamic assessment

Experimental investigation followed by thermodynamic assessment of the V-Zn system was carried out in the present study. A series of V-Zn alloys annealed at various temperatures were examined using scanning electron microscopy coupled with energy dispersive spectroscopy/wavelength dispersive X-ray spectrometer, X-ray diffraction and differential thermal analysis. It was confirmed that V Zn₁₆, with a V content of about 5.8 at.%, was indeed an equilibrium phase. DTA results indicated that the peritectic temperature for V Zn₁₆ was about 427 ^°C. Two new metastable compounds, V Zn₉ and V ₃Zn₂, with V contents of 8.5-11.3 at.% and 60 at.%, respectively, were discovered. DTA results together with SEM-EDS examinations revealed that V Zn₉ was formed at around 450 ^°C in Zn75V25 alloy with a cooling rate greater than 12 ^°C/min. The V Zn₉ phase, however, decomposed into V Zn₃ and liquid Zn when the alloy was held above 442 ^°C. The peritectic temperatures for two equilibrium phases, V ₄Zn₅ and V Zn₃, were 651 ^°C and 621 ^°C, respectively. These measurements were slightly lower than the values determined in prior studies. The onset temperature for forming V Zn₃ decreased significantly with increasing cooling rate while its exothermic peak widened during fast cooling. These phenomena indicated that both the nucleation and growth processes for V Zn₃ were kinetically challenged.In addition, the solubility of Zn in α-V was measured. It was 2.1 at.%, 2.5 at.%, 2.6 at.%, 2.9 at.% and 3.3 at.% at 450 ^°C, 600 ^°C, 670 ^°C, 800 ^°C and 1000 ^°C, respectively. Based on the results obtained in the present study and previous investigations, the V-Zn system was reassessed thermodynamically. The assessment was in good agreement with experimental results.     

Novel heat dissipation design for light emitting diode applications

The authors offer a new design in support of efficient heat dissipation for light emitting diodes (LEDs). In the first part of this paper we discuss improvements in LED packaging materials and layer assembly, and then describe the addition of a thin layer of electroplated copper to the LED base assembly to reduce thermal resistance and increase thermal diffusion efficiency. Also described is a three-dimensional finite element simulation that we performed to verify the proposed design (0.75, 1, and 3 W LED chip temperatures) and a LED heat transfer behavior analysis. The results indicate that the addition of a 9 mm² electroplated copper layer to the LED base assembly improved LED thermal dissipation by reducing chip temperature by 5°C compared to LEDs without the copper layer packaging. In the second part of this paper we describe (a) our heat pipe system/heat sink design for LED illumination, and (b) experiments in which we changed both working fluid mass and rotation angle to determine their effects on heat pipe cooling. Our results indicate that the most efficient heat dissipation occurred when an added heat pipe was arranged horizontally. Good heat dissipation was observed for heat pipes containing 2.52 g of water (temperature reduced by 50°C). Larger water volumes failed to dissipate additional heat due to the presence of steam inside the pipe.     

Simulation of solid thermal explosion and liquid thermal explosion of dicumyl peroxide using calorimetric technique

Dicumyl peroxide (DCPO), is produced by cumene hydroperoxide (CHP) process, is utilized as an initiator for polymerization, a prevailing source of free radicals, a hardener, and a linking agent. DCPO has caused several thermal explosion and runaway reaction accidents in reaction and storage zone in Taiwan because of its unstable reactive property. Differential scanning calorimetry (DSC) was used to determine thermokinetic parameters including 700 J g^–1 of heat of decomposition (ΔH_d), 110 °C of exothermic onset temperature (T₀), 130 kJ mol^–1 of activation energy (E_a), etc., and to analyze the runaway behavior of DCPO in a reaction and storage zone. To evaluate thermal explosion of DCPO with storage equipment, solid thermal explosion (STE) and liquid thermal explosion (LTE) of thermal safety software (TSS) were applied to simulate storage tank under various environmental temperatures (T_e). T_e exceeding the T₀ of DCPO can be discovered as a liquid thermal explosion situation. DCPO was stored under room temperature without sunshine and was prohibited exceeding 67 °C of self-accelerating decomposition temperature (SADT) for a tank (radius = 1 m and height = 2 m). SADT of DCPO in a box (width, length and height = 1 m, respectively) was determined to be 60 °C. The TSS was employed to simulate the fundamental thermal explosion behavior in a large tank or a drum. Results from curve fitting demonstrated that, even at the earlier stage of the reaction in the experiments, ambient temperature could elicit exothermic reactions of DCPO. To curtail the extent of the risk, relevant hazard information is quite significant and must be provided in the manufacturing process.     

Design,simulation and validation of a novel uncooled infrared focal plane array

This paper describes a novel single-layer bi-material cantilever microstructure without silicon (Si) substrate for focal plane array (FPA) application in uncooled optomechanical infrared imaging system (UOIIS). The UOIIS, responding to the radiate infrared (IR) source with spectral range from 8 to 14 μm, may receive an IR image through visible optical readout method. The temperature distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array, which is consisted of two materials with mismatching thermal expansion coefficients. In order to obtain a high detection to the IR object, gold (Au) film is coated alternately on silicon nitride (SiN_x) film in the flection beams of the cantilevers. And a thermal–mechanical model for such cantilever microstructure is proposed. The thermal and thermal–mechanical coupling field characteristics of the cantilever array structure are optimized through numerical analysis method and simulated by using the finite element simulation method. The thermal–mechanical rotation angle simulated and thermal–mechanical sensitivity tested in the experiment are 2.459 × 10⁻³ and 3.322 × 10⁻⁴ rad/K, respectively, generally in good agreement with what the thermal–mechanical model and numerical analysis forecast, which offers an effective reference for FPA structure parameters design in UOIIS.     

An uncooled optically readable infrared imaging detector

This paper presents a design and fabrication of bi-material micro-cantilever array (focal plane array, FPA) made of silicon nitride (SiN_x) and gold (Au) for uncooled optical readout infrared (IR) imaging system, in which silicon (Si) substrate is removed. Compared with the conventional thermal imaging detectors where the FPA must be put in high vacuum, IR thermal images can be obtained even though the cantilever array is placed in the atmosphere. The reason is the elimination of air gap (∼2 μm) between the cantilever beam and substrate, which introduces the air conduction of high temperature gradient. The preliminary experimental results with the micro-cantilever array of 140 × 98 elements and a 12-bit charge-coupled device (CCD) indicate that objects at temperature of higher than 120 °C can be detected and the noise-equivalent temperature difference (NETD) is ∼7 K. Also, the experimental results are well accordant with the thermomechanical analysis of designed micro-cantilever array.     

紫外热释电探测器的电学定标分析

在建立有效的紫外热释电探测器三维结构模型基础上,利用Ansys有限元软件的热分析功能,通过以不同的方式对模型施加模拟光辐射的热载荷和模拟电加热的热载荷,观察探测器热释电层的热传递过程并进行温度场分析。结果表明当以相同功率的光和电交替对探测器进行加热时,探测器将最终达到平衡;由于光和电加热的方式有所不同而会产生一定的误差。     

Solid-state potentiometric SO2 sensor combining NASICON with V2O5-doped TiO2 electrode

A compact tubular sensor based on NASICON (sodium super ionic conductor) and V₂O₅-doped TiO₂ sensing electrode was designed for the detection of SO₂. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al₂O₃ tube; furthermore, a thin layer of V₂O₅-doped TiO₂ with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V₂O₅ doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V₂O₅-doped TiO₂ sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO₂ in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO₂ concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO₂ against NO, NO₂, CH₄, CO, NH₃ and CO₂. Moreover, the sensor had speedy response kinetics to SO₂ too, the 90% response time to 50 ppm SO₂ was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO₂-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.     

Study of Electrical Conductance of Pressed Chemically Pure MnO2 Powder†

Variation of electrical conductance and capacity of chemically pure MnO₂ in pressed powder form under a stress 6·0 × 10¹¹ dynes/sq. cm has been studied within the temperature range 26^°c to 110^°c at 1 MC/s, Electrical conductance of samples in tablet, form (3 mm thick and 15 mm in diameter) was measured between 26^° C and 110^° before and after heat treatment at 300^°c for 36 hours. Capacitance values were also measured simultaneously within the above temperature range. Electrical conductance was found to attain a maximum at about 78^°c. There is a marked hysteresis in ‘; ln conductance’ ? 1 / T graph when measurements are made while temperature is rising and while falling.

Differential thermal analysis of the samo MnO₂ powder was also carried out. Measurements were made while heating and also while cooling. Two marked changes are clearly seen, one at mean temperature of 56^°c and the other at mean temperature of 80^°c, suggesting some second-order solid to solid phase changes at these temperatures. Corresponding breaks occur in the ‘ln conductance ’ ? 1/T and capacity-temperature graphs at the above-mentioned temperatures.     

A micro shear stress sensor based on laterally aligned carbon nanotubes

This paper reports the development of a micro thermal shear stress sensor that utilizes multiwalled carbon nanotubes as the sensing element. The sensor was fabricated by laterally aligning randomly distributed nanotubes into a 360 μm long and 90 μm wide conductive trace between two triangular shaped micro electrodes through the use of a high frequency AC electric field. During operation, the aligned nanotubes are electrically heated to an elevated temperature and surface shear stress is measured indirectly by the amount of convective heat transfer from the heated nanotubes to the surrounding fluid flow.The nanotube alignment process was primarily controlled by three different phenomena: dielectrophoresis, joule heating, and Brownian motion. Numerical simulations, together with experimental verifications, indicated that a successful alignment could only be realized if: (1) the dielectrophoretic force was positive, (2) the electro-thermal force was also positive, and (3) the dielectrophoretic force was high enough to overcome Brownian motion. The aligned nanotube trace has a room-temperature resistance of 580 Ω, which corresponds to a conductivity of 2.7 × 10⁴ S/m. The absolute temperature coefficient of resistivity ranges from 0.01 to 0.04% °C⁻¹. This is about one order of magnitude smaller than the highly doped polysilicon sensing material used in the MEMS micro shear stress sensor. The shear stress sensitivity of the nanotube trace operated at a 3% overheat ratio is found to follow the theoretical sensor power ∝ (shear stress)^1/3 relationship, provided the shear stress level is higher than 0.34 mPa. This result confirms the feasibility of using aligned multi-walled carbon nanotubes as a thermal shear stress sensing material.