New Thin-Film Multijunction Thermal Converter Design for Improved High-Frequency Performance

New thin-film planar multifunction thermal converters (PMJTC) were developed to improve the high-frequency ac-dc transfer differences. The heater resistor and thermocouples of these PMJTCs were produced on different substrates: an AIN chip for the heaters and polyimide film for the thermocouples, using simple fabrication processes. The thermocouples were moved from the conventional high-potential heater position, and placed close to the ground electrode of the input circuit. This new configuration upgrades the performance of ac-dc transfer differences above 10 kHz by improving both the electromagnetic coupling between the heater and thermocouples and the output resistance of thermocouples. Using a high thermal conductivity AIN substrate, through which heat is conducted from the heater to the hot junctions of the thermocouples, almost the same sensitivity as that of PMJTCs on silicon is obtained.     

Simulation and Fabrication of a Convective Gyroscope

In this paper, we present the simulation and fabrication of the gas gyroscope. The gas flow inside the hermetically packed sensor is simulated by utilizing 3-D transient compressible flow analysis. The pump working principle and the effect of the Coriolis acceleration on the laminar jet are validated by both analytical formulas and experiments. The sensor utilizes a new sensing element consisting of a thermistor heated by an interior heater, which is independently power-supplied. The sensor performance can be adjusted by the applied voltage on the heater. Both heater and thermistor are optimized in terms of thermal stress. The effect of thermal stress in a p-type silicon thermistor reduces the performance of sensor by 9.5%. The sensor has been calibrated and the role of the heater is verified.      

A Silicon Thermal Accelerometer Without Solid Proof Mass Using Porous Silicon Thermal Isolation

A Si thermal accelerometer without solid proof mass, based on porous silicon (PS) technology has been developed and characterized. The device is compatible with silicon technology and it consists of a polysilicon heater and two thermopiles, situated symmetrically on each side of a heater. A thick PS layer provides thermal isolation from the Si substrate. The operation principle is based on the movement induced thermal convection variations between the heater and the hot thermopile contacts, which are caused by the movement of the hot fluid medium on top of the heater with respect to the sensor die. A detailed simulation by the FEA package Ansys was carried out in order to find the optimum geometrical parameters and the theoretical device behavior. The porous silicon thermal accelerometer (PSTA) was tested in a specially designed vibration system for various frequencies and accelerations. Different packaging configurations were also evaluated for both air and oil surrounding environments. The dependence of the PSTA response on applied power was studied for each surrounding environment. In each case, the response was compared with a commercial reference accelerometer and the corresponding sensitivities were extracted.     

A novel thermal sensor concept for flow direction and flow velocity

This paper presents a unified theory for different measurement concepts of a thermal flow sensor. Based on this theory, a new flow sensor concept is derived. The concept allows measuring both direction and velocity of a fluid flow with a heater and an array of temperature sensors. This paper first analyzes the two-dimensional (2-D) forced convection problem with a laminar flow. The two operation modes of a constant heating power and of a constant heater temperature are considered in the analytical model. A novel estimation algorithm was derived for the flow direction. Different methods for velocity measurement were presented: the hot-wire method, the calorimetric method, and the novel average-temperature method. The only geometric parameter of the sensor, the dimensionless position of the sensor array, is optimized based on the analytical results. Furthermore, the paper presents the experimental results of the sensor prototype. In order to verify the analytical model, an array of temperature sensors was used for recording the 2-D temperature profile around the heater. Temperature values are transferred to a computer by a multiplexer. A program running on a personal computer extracts the actual flow velocity and flow direction from the measured temperature data. This paper discusses different evaluation algorithms, which can be used for this sensor. A simple Gaussian estimator was derived for the direction measurement. This estimator provides the same accuracy as the analytical estimator. Velocity results of both the calorimetric concept and the novel average-temperature concept are also presented.     

Development of thin-film multijunction thermal converters atPTB/IPHT

The thin-film multijunction thermal converter (PMJTC) developed in cooperation between Physikalisch-Technische Bundesanstalt (PTB) and Institut fur Physikalische Hochtechnologie e.V. (IPHT) is today's most sensitive and accurate standard for the precise measurement of electrical AC quantities in the frequency range of 10 Hz-1 MHz. Thin-film technology and micromechanics in silicon were essential for this success. The thin-film heater and bismuth/antimony thermocouples with high Seebeck effect deposited on a thin membrane of low heat conductance result in the attractively high sensitivity of the PMJTC which allows voltage measurements down to 100 mV to be performed. The statistics of the mass production of the PMJTCs show that PMJTCs built into a housing with an N-connector at the input can be reproducebly manufactured with an AC-DC voltage transfer difference smaller than 0.1 μV/V at 1 kHz, 8 μV/V up to 100 kHz, and below 40 μV/V up to 1 MHz for a heater resistance of 90 Ω. A compensation circuit has been added on the chip which results in low-frequency PMJTCs (LF-PMJTCs) with AC-DC transfer differences below 0.3 μV/V at 10 Hz     

Catalytic gas sensor with single-crystalline silicon heater

A single-crystalline silicon heater used in a catalytic sensor of the pellistor type qualitatively changes the pattern of active gas detection, which is related to a nonlinearity of the current-voltage (I-U) characteristic. The shift of the I-U curve toward lower values of the heater current allows both positive and negative components in the sensor response to be separated as determined by varying the bias voltage at a fixed value of the heater current. Under the action of carbon monoxide, the positive component of the sensor response exhibits a clearly pronounced maximum at a heater current of 28 mA and the height of this peak is proportional to CO concentration in a range of 0.5–2.0 vol %.     

Comparison of calibrated temperature sensors: 4–300 K

This paper discusses some serious discrepancies which arose between temperature measurements, as determined by calibrated, commercial temperature sensors, during the course of experiments designed to calibrate some locally-fabricated gold/chromel thermocouples. The three commercially-calibrated sensors were: a platinum resistor, a germanium resistor; and a silicon diode. The most serious discrepancies which occurred were between the results employing the silicon diode calibration, and the results from any of the other calibrations. We comment upon the procedures employed to achieve a reasonably self-consistent temperature calibration, and the suitability of the properties of gold/chromel thermocouples, for measurements over an extended range of cryogenic temperatures.     

A new optically sensed thermal element for precise AC-DC conversion

An optically sensed isothermal differential thermal converter has been reduced to practice using a commercially available optical infrared pyrometer. Eliminating the conventional bimetallic thermocouples avoids draining thermal energy from the heater, reduces the Thomson effect error, and minimizes shunt paths along the heater which bypass higher frequency signal components. The optically sensed thermal element provides the potential for greater accuracy over a wide frequency range, faster response time, and improved dynamic range over conventional wire or planar thermal elements using Seebeck, thermoresistive or semiconductor temperature sensing     

Bridge-output-to-frequency converter for smart thermal air-flowsensors

A fully integrated bridge-output-to-frequency converter has been realized as signal-conditioning circuitry for a one-chip smart thermal mass-flow sensor. The frequency converter reads out four separate resistor bridges of the air-flow sensor in order to realize high sensitivity and directional flow measurement over the full angle range of 360°. The converter selects the sensor bridges individually by means of a microprocessor-controlled analog multiplexer. The flow velocity and direction are also calculated by the microprocessor. The relative measurement cancels all first-order errors. The center frequency is 10 kHz and the sensitivity 1 Hz/(μV/V). A bridge-offset of 10 mV/V is allowed, and the linearity error is 0.1%     

Boron induced recrystallization of amorphous silicon film by a rapid thermal process

Rapid thermal process (RTP) is to induce boron-doped amorphous silicon into a high degree of crystallization of polycrystalline silicon in 5 min. In addition to the short time characteristic, it also provides a relatively lower temperature route to prepare high percentage of polycrystalline silicon in comparison with solid phase crystallization method. Before RTP, boron is homogeneously doped into the amorphous silicon film by ion implantation technology. After rapid thermal processing, the grain size of the polycrystalline silicon was found about at 0.1-0.5 μm. The degree crystallization of silicon is reached up to 99.1% with a good hole mobility of 138.6 cm²/V s.     

A silicon composite thermal and ionization X-ray detector

We have made a combination calorimetric and ionization X-ray detector by attaching a silicon p-i-n diode to a monolithic silicon microcalorimeter. Applying a bias to the diode enhanced the thermal signal, and with a reverse bias of 25 V we achieved a detection threshold of 8 eV, based upon energy scaling of the standard deviation of the baseline noise. We were able to measure a charge signal in the absence of applied bias on the diode, demonstrating that the junction potential is sufficient to drift the ionized charges to the contacts. A fraction of the electron-hole pairs created became trapped, manifested by excess broadening in the measured thermal signal and by using the variation of the thermal signal magnitude with reverse bias to fit for the fraction of charge that is trapped. The ability to collect charge without an applied bias is necessary to produce high resolution combination thermal and ionization detectors.     

Dynamic response analysis of pyroelectric sensitive element for thermal imaging

Temperature distributions under periodic thermal excitations and the responsivity of a pyroelectric device consisting of a cover layer, infrared absorber, metal contact, sensitive pyroelectric element, interconnecting column, and bulk silicon are found. Some results of numerical thermal modeling and analysis of exact expressions for a few extreme cases are presented. Pyroelectric responses of real structures are compared with the response of a single pyroelectric element in air as a limiting case of maximum sensitivity. The analytical approximations and numerical simulation show that the frequency response of the multilayered structure consists of different parts with simple frequency dependencies. In the region of high frequencies of light modulation, the responsivity is proportional to /spl omega//sup -1/, at low frequencies /spl sim/ /spl omega//sup -0.5/, and, in the region of intermediate frequencies, the voltage responsivity is independent of frequency.     

AeroMEMS Wall Hot-Wire Anemometer on Polyimide Substrate Featuring Top Side or Bottom Side Bondpads

Design, manufacturing, calibration, and basic characterization of a microelectromechanical systems (MEMS) wall hot wire sensor on a flexible polyimide substrate are presented. A configuration exhibiting bond pads on the top side of the foil, as well as an improved setup featuring a through-foil metallization and bottom side bond pads were established. Both sensor designs make use of a highly sensitive nickel thin-film resistor spanning a reactive ion etched cavity in a polyimide substrate. The polyimide base material enables the sensor to be adapted to curved aerodynamic surfaces, e.g., airfoils and turbine blades. A mismatch of curvature of aerodynamic surface and silicon sensor surface, as observed with previously presented MEMS hot-wire anemometers is avoided. The combination of polyimide's low thermal conductivity and a cavity featuring FEM-optimized dimensions accounts for a very low-power consumption (<25 mW). Fluctuations in wall shear stress up to 85 kHz can be resolved in constant-temperature mode. An average sensitivity of 0.166 V/(N/m²) is achieved in a wall shear stress range from 0 to 0.72 N/m². The specifically designed through-foil metallization process allows for electrical contacts to be positioned on the backside of the substrate, thus effectively minimizing aerodynamic disturbances.     

Flip-Chip Packaging for a Two-Dimensional Thermal Flow Sensor Using a Copper Pillar Bump Technology

A flip-chip packaged two-dimensional (2-D) thermal flow sensor fabricated in CMOS technology is presented. The sensor consists of polysilicon resistor heaters, Al/polysilicon thermopiles, and a substrate bipolar transistor located in the center of the sensor chip. The thermopiles and the transistor were used to measure the change of the flow-induced temperature distribution on the flow-sensing surface. The sensor chip was flip-chip packaged on a thin ceramic substrate using a copper pillar bump technology. The polysilicon resistor provides the necessary overheat of the chips, and thermal interactions with the flow are achieved via the pillar bump and the thin ceramic substrate. The operating principle for the packaged sensor remains the same as before packaging. The backside of the ceramic substrate provides a smooth surface for the sensor to be exposed to the flow. Meanwhile, the ceramic substrate holds the sensor chip and protects it from being contaminated or even destroyed by the corrosive environment. The packaged flow sensor shows the good performances compared with the unpackaged sensors. It can detect airflow speed up to 30 m/s with accuracy of 0.5 m/s and airflow direction in a full range of 360 with an accuracy of 6 at room temperature.     

电阻热效应对力式微固态测风传感器测量精度的影响

本文就电阻热效应对基于风的拖动力原理的微型固态测风传感器测量精度的影响进行了研究.微型固态测风传感器通过溅射在悬梁上的铂电阻测量悬梁弯曲应变来获得风速信息和简单的风向信息.风吹过铂电阻时,除了应变引起电阻阻值变化外,由于热传导、对流、辐射等热效应,其阻值也会随着风速的变化而变化.当热效应引起的电阻的变化趋势和应变引起的电阻变化趋势相反时,传感器的输出先减小后增大,风速测量产生较大误差.文中对两种铂电阻在悬梁上的放置连接方式的传感器进行了理论分析,通过对利用MEMS工艺制作的两种传感器的测试,证实理论分析与实验结果相符.     

Effect of Thin Film Thicknesses and Materials on the Response of RTDs and Microthermocouples

Fabrication and thermal characterization of a resistance temperature detector (RTD) heater and microthermocouples (MTs) on silicon substrates have been reported in this paper. The influence of film thickness and nickel-gold (Au) electroplating on RTD on its steady-state temperature with respect to its steady-state electrical power input and resistance is studied. Further, the thermal effects of multiple thermocouples in a thermopile as well as the effects of Au layers in the contact pads of the thermopiles on their open-circuit Seebeck voltage are studied. Therein lies the novelty of this paper. The in situ operating relationships for the RTD heater and the MT are provided     

Microhotplate Temperature Sensor Calibration and BIST

In this paper we describe a novel long-term microhotplate temperature sensor calibration technique suitable for Built-In Self Test (BIST). The microhotplate thermal resistance (thermal efficiency) and the thermal voltage from an integrated platinum-rhodium thermocouple were calibrated against a freshly calibrated four-wire polysilicon microhotplate-heater temperature sensor (heater) that is not stable over long periods of time when exposed to higher temperatures. To stress the microhotplate, its temperature was raised to around 400 °C and held there for days. The heater was then recalibrated as a temperature sensor, and microhotplate temperature measurements were made based on the fresh calibration of the heater, the first calibration of the heater, the microhotplate thermal resistance, and the thermocouple voltage. This procedure was repeated 10 times over a period of 80 days. The results show that the heater calibration drifted substantially during the period of the test while the microhotplate thermal resistance and the thermocouple-voltage remained stable to within about plus or minus 1 °C over the same period. Therefore, the combination of a microhotplate heater-temperature sensor and either the microhotplate thermal resistance or an integrated thin film platinum-rhodium thermocouple can be used to provide a stable, calibrated, microhotplate-temperature sensor, and the combination of the three sensor is suitable for implementing BIST functionality. Alternatively, if a stable microhotplate-heater temperature sensor is available, such as a properly annealed platinum heater-temperature sensor, then the thermal resistance of the microhotplate and the electrical resistance of the platinum heater will be sufficient to implement BIST. It is also shown that aluminum- and polysilicon-based temperature sensors, which are not stable enough for measuring high microhotplate temperatures (>220 °C) without impractically frequent recalibration, can be used to measure the silicon substrate temperature if never exposed to temperatures above about 220 °C.     

The use of rapid thermal annealing for studying contamination in silicon

Contamination of silicon wafers by transition metals is known to degrade device performance sharply. Transition metal contamination can arise from several sources. Here, we present a fast method to detect contamination consisting of the combination of rapid thermal annealing which is known to activate metallic impurities and diffusion length measurements by the surface photovoltage technique which needs no permanent contacts.     

Single-mode rib optical waveguides on SOG/SU-8 polymer and integrated Mach-Zehnder for designing thermal sensors

This paper presents a successful design, realization,and characterization of single-mode rib optical waveguides on SOG/SU-8 polymers in order to highlight a new approach to designing heat sensors. The basic principle of this new thermal-sensing method relies on the differential thermal behavior regarding both acting arms of a micro Mach-Zehnder Interferometer(MZI). First, two families of single-mode straight rib waveguides composed of SOG/SU-8 polymers are analyzed. Hence, optical losses for TE/sub 00/ and TM/sub 00/ optical modes for structures on Si/SiO/sub 2//SU-8 have been estimated respectively as 1,36 /spl plusmn/ 0,02 and 2,01/spl plusmn/0,02 dB/spl middot/cm/sup -1/, while the second one composed of Si/SiO/sub 2//SOG/SU-8 presented losses of 2,33 /spl plusmn/ 0,02 and 2,95/spl plusmn/0,02 dB/spl middot/cm/sup -1/. Then, owing to modeling results, an experimental sensor is realized as an integrated device made up of SU-8 polymer mounted on a standard silicon wafer. When subjected to a radiant source, as a laser light (980 nm) is injected across the cleaved input face of the MZI, the significant change of output signal allows us to consider a new approach to measuring radiant heat flowrate. Experimental results are given regarding the obtained phase shift against the subjected thermal power. According to the modeling results, one can expect new highly sensitive devices to be developed in the next coming years, with advantageous prospective industrial applications.     

A controllable and byproduct-free synthesis method of carbon-coated silicon nanoparticles by induction thermal plasma for lithium ion battery

Carbon coated silicon nanoparticle is regarded as a promising anode material for the next generation of lithium ion batteries, while the development of a cost-effective and environmental-friendly preparation method is still difficult and hinders the practical implementation. In this research, a controllable and byproduct-free synthesis method is proposed for the preparation of silicon nanoparticles with amorphous hydrogenated carbon coating. The current apparatus is operated based on the application of induction thermal plasma. Plasma properties are tunable by adjusting the ratio of tangential and radial gas flow rates (T/R), which compose the plasma sheath gas. Obtained results reveal the plasma shape is shrunk with higher T/R values, which will lead to a steeper temperature gradient and lower temperature distributions in reaction chamber. Consequently, the compositions and properties of synthesized particles can be modified with T/R values. The formation of SiC, which was an intractable issue before, can be vanished at higher tangential gas flow rates in current research and the capacity of silicon anode for batteries will be improved in predict. This research is significant for a deep understanding of plasma synthesis processing and design of batteries with excellent performance.