Impact of thermal contact resistances on micro-gap heat losses for microthermionic power generators

Thermionic power generation is a safe and clean energy source that allows for converting heat into electrical energy using thermionic electrons. The miniaturization is an advantage of this technology that led to the recent development of micro-gap thermionic power generators. In this work, thermal contact resistances between the micro-gap insulators and the emitter as well as between the micro-gap insulators and the collector are measured. A thermal resistance of 48.6 K/W is obtained by downsizing the insulators until 60 × 45 μm² of contact area with the emitter, demonstrating a high impact for decreasing the micro-gap conduction heat loss density from the emitter to the collector from 28 W/cm² (theoretical value obtained without considering contact resistances) to 5.6 W/cm². Downsizing the contact area between the insulators and the emitter from 320 × 300 to 60 × 45 μm² leads to an increase of the power conversion efficiency from 9.1 × 10^?5 until 1.5 × 10^?3.     

A full high-definition quantum dot light-emitting diode-on-silicon microdisplay

We report a 0.39-in. quantum dot light-emitting diode (QLED) microdisplay with full high-definition (FHD, 1920 × 1080) resolution by integrating a red top-emitting QLED on a complementary metal–oxide–semiconductor (CMOS) backplane. By optimizing the microcavity structure and constructing a suitable energy-level structure for the QLED devices, the performance of the large-area (4.9 × 8.7 mm²) top-emitting device with normal structure reached 13,936 cd/m² of brightness at 5-V bias with 13.3% external quantum efficiency (EQE). Notably, the optimal device showed a low turn-on voltage of 1.7 V, which matched well the voltage output of the CMOS backplane. Our work demonstrates the great promise of QLED microdisplays for applications in head-mounted augmented reality/virtual reality (AR/VR).     

Development and characterization of a microthermoelectric generator with plated copper/constantan thermocouples

This work reports the development and the characterization of a microthermoelectric generator (μTEG) based on planar technology using electrochemically deposited constantan and copper thermocouples on a micro machined silicon substrate with a SiO₂/Si₃N₄/SiO₂ thermally insulating membrane to create a thermal gradient. The μTEG has been designed and optimized by finite element simulation in order to exploit the different thermal conductivity of silicon and membrane in order to obtain the maximum temperature difference on the planar surface between the hot and cold junctions of the thermocouples. The temperature difference was dependent on the nitrogen (N₂) flow velocity applied to the upper part of the device. The fabricated thermoelectric generator presented maximum output voltage and power of 118 mV/cm² and of 1.1 μW/cm², respectively, for a device with 180 thermocouples, 3 kΩ of internal resistance, and under a N₂ flow velocity of 6 m/s. The maximum efficiency (performance) was 2 × 10^?3 μW/cm² K².     

Implications of microcavity plasma devices for new plasma‐display‐panel cell structures with improved luminosity

Abstract— The unique properties of microcavity plasma devices, and their potential to provide the basis for alternative PDP cell structures of improved luminosity, are described. Arrays as large as 500 × 500 (250,000) inverted pyramid microcavity devices, each with an emitting aperture of 50 × 50 μm² and designed for AC or bipolar excitation, have been fabricated in Si and operated in the rare gases and Ar/N₂ mixtures at pressures up to and beyond 1 atm. For a device pitch of 100 μm, the array filling factor is 25% and the device packing density is 10⁴ cm^?2. Measurements of the unoptimized radiant output of 500 × 500 arrays of Si microplasma devices, operating in Ne/(5–50)% Xe mixtures and photoexciting (in transmission mode) a 20‐μm‐thick film of green phosphor, yield values of the luminous efficacy up to 7.2 ± 0.6 lm/W for a Ne/50% Xe mixture (total pressure of 800 Torr) excited by a 20‐kHz sinusoidal voltage waveform. Sustaining voltages ranging from ～250 to 340 V (RMS) yield luminance values up to ～2000 cd/m² for Ne/50% Xe mixtures but the incorporation of field emitters or MgO into the microcavity is expected to significantly reduce the required operating voltage. Also, the fabrication of microplasma devices in ceramic multilayer structures or glass for scaling the display area is discussed briefly. Recent laser spectroscopic measurements of Xe(a ³Σ_u⁺) absorption in the visible and near‐infrared suggest steps to be taken in PDP cell design, particularly as the Xe content in Ne/Xe mixtures is increased.     

A MEMS-based thermal infrared emitter for an integrated NDIR spectrometer

A novel micromachined thermal infrared emitter using a heavily boron doped silicon slab as radiating element is presented. The fabrication process has been designed to allow the integration of such infrared emitters with an array of thermopile infrared detectors, with the aim of achieving an integrated non-dispersive infrared microspectrometer. A first set of infrared emitters with a common size for the doped silicon radiating slab (1,100?×?300?×?8?μm³) has been successfully fabricated and characterized. The working temperature of the Joule-heated radiating slabs has been controlled by means of DC and pulsed electrical signals, achieving temperatures well beyond 700°C. The thermal time constant measured in pulsed operation, around 50?ms, is adequate to enable the direct electrical modulation of the emitted radiation up to a frequency of 5?Hz while maintaining the full modulation depth. The temperature distribution in the radiating elements has been analyzed using two different thermal imaging methods.     

Machine learning technique based extremely broadband small‐signal behavioral model for InP DHBTs

A novel modeling methodology for indium phosphide (InP) double heterojunction bipolar transistors (DHBTs) based on the theory of Bayesian inference, a well‐known method from the field of machine learning, is presented in this article. An extremely broadband small‐signal behavioral model, from 200 MHz to 325 GHz, is built, tested, and validated in this work, with excellent agreement obtained between the extracted model and the experimental data in the form of S‐parameters. A single finger InP DHBT device, with emitter size of 0.5 × 5 μm² exhibiting an ft of over 550 GHz, is used in the verification example. Taking advantage of regression techniques based on machine learning concepts, the proposed black‐box behavioral model can more accurately predict the behavior of the device compared with the traditional equivalent circuit modeling method. Several sets of measured vs modeled data are shown, indicating the efficacy of the method.     

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Abstract— An active‐matrix organic light‐emitting diode (AMOLED) display driven by hydrogenated amorphous‐silicon thin‐film transistors (a‐Si:H TFTs) on flexible, stainless‐steel foil was demonstrated. The 2‐TFT voltage‐programmed pixel circuits were fabricated using a standard a‐Si:H process at maximum temperature of 280°C in a bottom‐gate staggered source‐drain geometry. The 70‐ppi monochrome display consists of (48 × 4) × 48 subpixels of 92 ×369 μm each, with an aperture ratio of 48%. The a‐Si:H TFT pixel circuits drive top‐emitting green electrophosphorescent OLEDs to a peak luminance of 2000 cd/m².     

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 MEMS-based gas chromatography column with integrated micro heater

A high-performance MEMS-based gas chromatography (GC) device is proposed comprising a miniature serpentine column with dimensions of 3.2 m × 200 μm × 250 μm (length × width × depth) and with an integrated Pt micro heater. The column is fabricated on a Si die measuring 3.5 × 1.8 mm² using a wet etching process and is bonded to a Pyrex cover plate incorporating the Pt micro heater via a thermal fusion process. The experimental results reveal that an applied voltage of 9.7 V is sufficient to maintain a constant temperature of 85°C for elution purposes. In addition, it is shown that the proposed device successfully detects the concentrations of both pure and mixed samples of four volatile organic compound gases, namely acetone, toluene, methanol, and benzene. Finally, the theoretical plate number obtained by the proposed MEMS-based GC device is shown to be 2–3 times higher than that obtained from a conventional capillary-based GC system under the same injection conditions.     

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.

     

Ga‐doped zinc oxide: An attractive potential substitute for ITO,large‐area coating,and control of electrical and optical properties on glass and polymer substrates

Abstract— Ga‐doped ZnO (GZO) films with thicknesses of 30–560 nm were prepared on glass substrates at 200°C by ion plating with direct‐current arc discharge. The dependences of the characteristics of GZO films on thickness were investigated. All the polycrystalline GZO films, which showed high transmittance in the visible region, were ZnO crystallites with a wurtzite structure highly oriented along the (0002) plane. The resistivity, ρ, of GZO films decreases with increasing film thickness. The highest ρ achieved is 4.4 × 10⁻⁴ Ω‐cm with a carrier concentration, n, of 7.6 × 10²⁰ cm⁻³ and a Hall mobility, μ, of 18.5 cm²/V‐sec, determined by Hall effect measurement for the GZO films with a thickness of 30 nm, and the lowest ρ is 1.8 × 10⁻⁴ Ω‐cm with n = 1.1 × 10²¹ cm⁻³ and μ = 31.7 m²/V‐sec for the GZO film with a thickness of 560 nm. In addition, highly transparent GZO films with thicknesses of 12–300 nm were fabricated on unheated polymethyl methacrylate (PMMA). The ρ of these transparent GZO films decreased from 20 to 4 × 10⁻⁴ Ω‐cm with film thickness.     

A high-luminance and high-resolution CRT for projection HDTV display

Abstract— We have developed a 3-in. YAG (yttrium aluminum garnet) projection CRT for an HDTV display. The densely packed phosphor screen with a multi-layer interference filter is prepared by depositing phosphor on a YAG faceplate using a centrifugal sedimentation method. The tube's envelope is made from a glass whose expansion coefficient is well-matched with that of YAG. The focusing characteristics of an optimally designed pre-focusing electron gun and focusing magnet are improved for a HDTV display application. As a result, the green, red, and blue tubes reached luminances of 1.4 × 10⁵, 6.2 × 10⁴, and 8 × 10³ cd/m² at a cathode current of 1.0 mA and an anode voltage of 29 kV, respectively, with a half-intensity linewidth of 85 μm. An experimental 48-in. rear-projection TV set using the YAG projection tubes achieves more than 1000-TV-lines horizontal resolution and 300-cd/m² mean white luminance.     

Development of high‐brightness flat field‐emission lamp with a special electrode system for block dimming BLUs for LCDs

Abstract— A flat field‐emission lamp (FFEL) has been developed that utilizes a specially designed electrode structure and an unique nanostructure carbon electron emitter called a carbon nanometer electron exit (CNX) emitter. CNX emitters have been developed on metal‐wire substrates with a special plasma chemical‐vapor‐deposition technique. Field electron emission from CNX emitters has been investigated in a vacuum of 2×10^?4 Pa by using a diode configuration with an A–K space of 1 mm, which shows that an emission current of 5.7 A/cm² can be obtained at an electrical‐field strength of 2.2 V/μm. Then, the emission‐current stability was also carried out to investigate the CNX‐emitter lifetime. Also, scanning electron microscopy (SEM) and micro‐Raman spectrum was used to characterize the CNX film. Furthermore, the design of the special diode emission system was optimized by simulating the electron orbits with a commercial software, the result of which indicates that the emission system was used to effectively extract electrons from the emitter and control the local block dimming. And, also, a simple FFEL structure was used to illustrate the simulation results. Finally, a 7‐in. FFEL has been successfully fabricated, demonstrating a luminance of 15,000 cd/m² with an anode voltage of 6 kV.     

An ultra low power CMOS based temperature to digital converter in 0.045 µm technology

This research propose a VLSI based temperature to digital converter (TDC) which is implemented with the aid of CMOS technology whose precise functionality is to sense the temperature-dependent source-gate voltage (V_SG) of PMOS Transistor. It measures an inaccuracy of ±40 mK on 20 samples from one batch ranging between −60 °C to +60 °C temperature. This result is mainly due to the generation of pmos transistors drain currents which minimizes the spread in their gate to source voltages in addition to a PTAT digital circuit in support of the proper stretch in the pmos transistors emitter currents. The entire design has been implemented in 0.045 µm technology and draws a current of 0.3 µA which shows that the proposed TDC can be considered as ultra-low power device as the power consumed by it is 18.09E-12 W between the room temperatures of −60 °C to +60 °C. As per the accuracy of the proposed TDC the calibration cost can be reduced which would avoid the difficulty in the batch calibration. The supply voltage given to the device is 0.45 volts and a temperature inaccuracy of ±18 mk is achieved.     

用于低温环境的铂电阻温度微传感器

目前,铂电阻温度传感器主要应用于73 K(-200℃)以上环境的温度检测。设计了可用于10 K(-263℃)～200 K(-73℃)低温区的铂电阻温度微传感器。铂电阻温度微传感器采用对称的折回型结构,这种结构有效地降低了交流感抗的影响。传感器的敏感薄膜是一层采用磁控直流溅射沉积厚度为200 nm的铂薄膜。采用QD PPMS仪器测试传感器的电阻与温度的变化关系,得出传感器的电阻温度系数(TCR):研制的温度传感器的电阻温度系数在温度高于30K(-243℃)时可达到9980×10-6/K,同时在低于30K(-243℃)的深低温区域TCR也可达到3730×10-6/K。     

基于BiCMOS工艺可修调的高精度低温度系数带隙基准源设计

设计了一种利用电阻比值校正一阶温度系数带隙基准电路的非线性温度特性来实现低温度系数的高精度低温度系数带隙基准源;同时设置了修调电路提高基准电压的输出精度.该带隙基准源采用0.8μm BiCMOS(Bipolar-CMOS)工艺进行流片,带隙基准电路所占面积大小为0.04 mm2.测试结果表明:在5 V电源电压下,在温度-40℃～125℃范围内,基准电压的温度系数为1.2×10-5/℃,基准电流的温度系数为3.77×10-4/℃;电源电压在4.0 V～7.0 V之间变化时,基准电压的变化量为0.4 mV,电源调整率为0.13 mV/V;基准电流的变化量为变化量约为0.02μA,电源调整率为6.7 nA/V.     

基于铂电阻的温度高精度测量研究

针对采用铂电阻对温度进行高精度测量,从硬件电路和曲线拟合2个方面进行了研究。电路上采用同一个电压给传感器恒电流驱动电路和A／D转换电路作参考电压,保证了温度检测的精度,并用最小二乘法直接拟合了描述采样值一温度关系的曲线,弥补了Pt100测温时信号从铂电阻到A／D转换的过程中各个中间环节所产生的偏差。该方法可使测量偏差优于0．05℃,并已在研制的高精度温度温差控制系统中得到应用。     

Non-intrusive measurement of microscale temperature distribution by spontaneous Raman imaging

A non-intrusive and spatially resolved temperature measurement technique based on spontaneous Raman imaging was developed to measure two-dimensional temperature distributions in microfluidic systems. Raman scattering arising from OH stretching vibrations of H₂O molecules was used to measure the local channel flow temperature because of its high sensitivity to temperature. The OH stretching band has two parts with contrasting temperature dependences: hydrogen-bonded (HB) and non-hydrogen-bonded (NHB) modes. Raman images of HB and NHB modes were separately captured by an electron-multiplying charge-coupled device camera using two bandpass filters with center wavelengths of 642 and 660 nm, respectively. The two-dimensional temperature distributions were obtained from the intensity ratio of the two images by applying a calibration curve, which showed that there was a linear relationship between the temperature and the intensity ratio of HB to NHB modes for temperatures in the range 293–333 K. Temperature distribution measurements were demonstrated in the mixing flow field in the junction area of a T-shaped channel composed of a poly(dimethylsiloxane) chip and borosilicate glass slides. Non-uniform temperature distributions were quantitatively visualized at a spatial resolution of 12.8 × 12.8 μm² for three different heating conditions.     

Passively addressed FLC display possessing an inherent gray scale and memory

Abstract— A passively addressed 64 × 64 ferroelectric liquid‐crystal display (FLCD) has been developed. The display matrix has a 33 × 33 mm² aperture, and the FLC layer thickness is 5.2 ± 0.2 μm. The display device operates with a frame frequency of 30 Hz (at V_row = ±18 V, V_col = ±9 V, T = 23°C), generating a continuous gray scale which can be memorized for more than 10 days after the driving voltage is switched off. A new approach for multiplex electronic addressing of the FLCD gray scale is proposed. The conditions of the hysteresis‐free gray‐scale generation for multiplex addressing and the gray‐scale memorization after the voltage is switched off, as well as the time steadiness of memorized images, are considered.