Jin-Shown Shie

High performance Pirani vacuum gauge

As an extension of previous work in our laboratory, a wide‐range Pirani gauge that is capable of measuring vacuum pressure down to 10−7 Torr reproducibly has been built. The micromachined Pirani sensor used in the experiments has a suspended membrane that is supported by the nearly radiation‐limited, thermally insulating beam leads crossing over a V‐groove cavity. A method of partial dummy compensation, as proposed previously by Weng and Shie for eliminating the ambient drift, is proved here to be very effective with a thermal drift as small as only 5.7 μV/°C. It has also been found that a thermal‐stress‐induced piezoresistive effect, which has a profound influence on the limitation of measurement, appears in the constant‐bias operation wherein the sensor temperature rises with the reduction of gas pressure and therefore thermal conduction. This effect causes the irreproducibility of pressure measurements by the device below 10−5 Torr. In addition to its inherently higher sensitivity, a constant‐temperatu...

Characterization and modeling of metal-film microbolometer

The characteristic thermal parameters of a platinum-film microbolometer are extracted from the data of two measuring methods. A simple and accurate equivalent circuit model, along with its thermal behavior, is proposed for the device. Applying the model to simulate some device circuits results in good agreement with the experimental data. Furthermore, an effective method of ambient temperature compensation, proposed previously by our laboratory, is demonstrated both experimentally and by simulation using the same model. The established electro-thermal model therefore serves as an useful tool for SPICE simulations in the design of microbolometers.

Wafer bonding by low-temperature soldering

Abstract Recently, wafer level packaging received lots of attention in microsystems because it shows the potential to reduce the packaging cost, while the yield of devices after dicing and packaging can be increased. However, there is a limitation of commercialized wafer bonding technology, i.e., the high process temperature, such as 1000°C of silicon fusion bonding, and 450°C of anodic bonding. A novel low-temperature wafer bonding with process temperature lower than 160°C is proposed, it applies the In–Sn alloy to form the interface of wafer bonding. The experiment results show helium leak test of 6×10 −9 Torr l/s, and a tensile strength as high as 200 kg/cm 2 . Reliability test after 1500 temperature cycles between −10°C and 80°C also shows no trace of degradation compared to the initial quality of the samples. This low-temperature soldering process demonstrates its promising potential at the wafer level packaging in industrial production.

A sensitive Pirani vacuum sensor and the electrothermal SPICE modelling

Abstract A sensitive micro-Pirani vacuum sensor has been fabricated. With effective schemes of ambient-temperature compensation and stabilization, it is capable of measuring vacuum pressure linearly from 1 torr down to 10 −7 torr, a three orders-of-magnitude improvement in resolution over conventional gauges. A special electrothermal SPICE model, complementary to the conventional analog representation of thermal parameters, is also proposed. It allows a high-level sensor-circuit integrated simulation based on the most fundamental principle and thermal variables. Good agreement between the measured data obtained from a constant-temperature readout circuit and the simulation result is demonstrated.

Micromachining on (111)-oriented silicon

Micromachining on (111)-oriented silicon in various alkaline solutions was studied. By means of spoke and donut-like etching patterns, the experiment shows that 〈110〉 directions have the highest etch rate and the final emergent periphery is hexagon bounded on the bottom surface plane. The six sidewalls are defined by {111} planes, which can be derived from its crystal geometry, having three facets with inclining angles of 70.5° and another three with declining angles of 109.5° respect to the (111) surface plane. SEM pictures show that aqueous KOH solution results in smooth surface morphology due to its higher etch rate of residual oxide existed in the silicon, while the other etchants such as hydrazine (N2H4) and tetramethyl ammonium hydroxide (TMAH) induce seriously wavy roughness. Moreover, various concentrations of KOH solution have been studied to determine the (110)/(111) etch ratio, and the ratio more than 100 were demonstrated. Using this method, suspended single-crystal silicon (c-Si) microstructures were fabricated for some potential uses such as thermopile, silicon bolometer, mass flow transducer and other force microsensors. As an application example, shallow-gap μ-Pirani vacuum sensor demonstrated its high pressure measuring capability as high as 103 Torr.

An innovative Pirani pressure sensor

A conventional Pirani vacuum sensor is converted into a device able to measure high gas pressure. By referring to infinite pressure, heat-loss change from the reference to a measured pressure induces electrical signal on the resistive sensor. 0.3 /spl mu/m shallow gap is formed for the floating microsensors to increase its sensitivity. This results in a measurable range from 10/sup 5/ down to 10/sup -1/ Torr. The thermal microsensor differs from the piezoresistive or capacitive type in sensing mechanisms. It also has advantages in smaller size and simpler structure.

Fabrication of low-stress dielectric thin-film for microsensor applications

A method of fabricating low-stress dielectric thin film as the supporting material of micromachined devices is reported. The film is processed by post thermal oxidation of silicon-rich nitride (SN) deposited on a silicon substrate by LPCVD. Due to the compensation on the nitride by its top oxide, an ultra-low residual stress less than 10 MPa can be obtained with a proper oxidation scheme. Characteristics of the oxidized nitride were analyzed by Auger electron spectroscopy (AES) and ellipsometry. Large floating membranes of 4/spl times/4 cm/sup 2/ and 400-nm thick can be made by this method with TMAH etching.

Parameter extraction of resistive thermal sensors

Abstract Obtaining thermal parameters is important in evaluating the performance of thermal microsensors. Two experimental methods are described here for the study of the pressure-dependent thermal behavior of the sensors: a bolometric method that utilizes a chopped light input to obtain a sensor frequency response, and deriving its thermal data therefrom; a.d.c. electrical method that measures the heat required for balance under d.c. bias, and obtaining sensor information. The thermal conductance and capacitance, absorptance, as well as emissivity of a sensor can be extracted from the experimental measurements. These parameters provide the essential data for the electrothermal SPICE program in the related design simulations.

AQUEOUS PHOTOLITHOGRAPHIC ETCHING OF TGS

Abstract The solubility and the etching rate (b-face) of TGS crystal in acetone- and ethyl alcohol-water solutions were studied. With the etching knowledge and the photolithographic technique, it is feasible to make TGS pyroelectric detectors of select-etched structure, which is advantageous in processing handling and tooling, together with high detector sensitivity resulting from controllable thinner thickness and better thermal insulation of active area.

Parameter extraction of resistive thermal microsensors by AC electrical method

Obtaining device parameters of thermal microsensors is essential for evaluating their performances and simulation modeling. We report an ac electrical method for extracting these parameters experimentally with relatively simple instrumentation. The basic parameters of resistive microsensors, the resistance, temperature coefficient of resistance, thermal capacitance, and conductance, are derivable from the second harmonic signal of the output voltage induced by a sinusoidal driving current. The results are compared with other methods.