Chih-Hsiung Shen

A Novel Two-Axis CMOS Accelerometer Based on Thermal Convection

Accelerometers based on thermal convection use a tiny bubble of heated air and pairs of temperature sensors hermetically sealed inside the sensor package cavity. In this paper, we successfully design and fabricate a novel thermal-bubble-based micromachined accelerometer with the advantages of minimized solid thermal conductance and higher sensitivity. The proposed accelerometer consists of a microheater and two pairs of thermopiles floating over an etched cavity and is constructed by our proposed microlink structure. Two-dimensional acceleration detection is easily realized using the microlink structure, and it can be applied to the technology of inclinometers, anemometers, and flowmeters. The heater and thermopiles are connected by netlike microlink structures, which enhance the structure and greatly reduce the solid heat flow from the heater to the hot junctions of the thermopiles. The samples are fabricated by the TSMC 0.35-mum 2P4M CMOS process, which has been provided by the national chip implementation center (CIC). Our design has proved to be applicable for commercial batch production with outstanding strong structures and uniform quality. We measure the output signal by inclining the sensor to evaluate the performance of this accelerometer. The best sensitivity of 22 muV/g was obtained from acceleration versus output voltage under several experimental conditions.

A new approach of thermal type microsensor with photonic crystal

A new idea of improving complementary metal-oxide-semiconductor (CMOS) thermopile performance is introduced to increase the absorption of infrared radiation by leading the photonic crystal (PC) into thermopile in this paper. A highly sensitive infrared detector requires an excellent signal induced by incident IR radiation to maximize the temperature change. A photonic crystal structure offers significantly effect for absorption of infrared radiation. Firstly we develop such a structure of thermopile with high performance by using 0.35µm 2P4M CMOS IC compatible process which can be easily and exactly fabricated. Several designs of infrared microsensors are proposed to study influential parameters from photonic crystal structure. The measurement results show these devices get greatly responses higher than the thermopile without photonic crystal. To that end, an optimal parameter is acquired at the same time. Our design is proved to be adequate for commercial batch production.

A novel magnetic-catalytic CMOS MEMS compatible gas sensor with ultra low power consumption

Beyond the conventional chemical sensors with heating power, we proposed a total new magnetic-catalytic sensing mechanism without heating which includes the original sensing material and also magnetic-catalytic with even higher sensitivity than before. A magnetic material in sol-gel method and a prepared solution of sol-gel SnO2 is mixed at SnO2 : Fe3O4 = 3 : 1. The samples with several pH conditions were under test and verified inside a CO gas chamber with solenoidal coils. The sensitivity of proposed monoxide sensor reaches 0.3416%/ppm under 18.2 Gauss without heating which shows applicable for an ultra low power CO sensor with high sensitivity.

A low cost high sensitivity CMOS MEMS gas sensor

A CMOS micromachined gas with advantages of CMOS standard process and high sensitivity is presented in this paper. The proposed gas sensor was built with array of floating membranes and serially connected over an etched cavity. Finger type electrodes are built for sensing the resistance of coated sensor material. A proposed highly integrated multi-layer structure of electrodes is formed with metal/via layers in series to derive a lower and stable resistance of sensing material. The micro heater of n-type polysilicon with 4.2 kΩ is situated beneath each active area of the membrane to obtain a stable working temperature with an 120µW power consumption. The sensing material SnO2 was deposited onto the electrodes after sol-gel formation. Furthermore, the samples are fabricated by TSMC 0.35µm 2P4M CMOS process which is provided by CIC with outstanding strong structures and high sensing performance with the minimum CO concentration under 4ppm. The experimental measurement shows the research is applicable for a low cost CO sensor with enough sensitivity.

A New Structure for CMOS Thermal-Bubble-Based Accelerometer

In this paper, we design and fabrication a novel thermal-bubble-based micromachined accelerometer with advantages of minimum solid thermal conductance and high sensitivity successfully. It can detect two-dimension acceleration changed and apply to technology of inclinometers, anemometers and flow meters. A new accelerometer consists of a micro heater and two pairs of thermopiles floating over an etched cavity that is constructed by our proposed micro-link structure. The heater and the thermopiles are connected by network-like structure of micro-links, which enhance the structure and greatly reduce the solid heat flow from the heater to the hot junctions of thermopiles. The samples are fabricated by TSMC 0.35 mum 2P4M CMOS process which is provided by CIC with outstanding strong structures and uniform quality. Our design is proved to be adequate for commercial batch production. We measure the output signal by inclining the sensor to evaluate the performance of this accelerometer. The measurement shows the output signal is inverse proportional to the tilt angel and the output voltage is increased when the input power increases. Furthermore, the sensitivity was obtained for acceleration vs. output voltage with an average slope of 0.325 muV/g in this case.

A New High-Filling-Factor CMOS-Compatible Thermopile

To reach a high fill factor, a new CMOS-compatible thermopile was designed and fabricated. The floating membrane of the thermopile that we designed was formed by a T-shape anisotropic etching window with a minimum etching area. The design and fabrication of thermopile sensors are realized by using 1.2-mum CMOS IC technology combined with a subsequent anisotropic front-side etching. The proposed T-shape etching windows are designed at four quadrants of a membrane to form the extended undercut etching area of opened windows of overlap. The floating membrane has a larger area of 1100 times 1100 mum2 and is 2 mum thick. The area of the proposed membrane is increased by about 21.5%, which absorbs more infrared radiation than the conventional design and enhances responsivity very well, as shown in the measurement. A surface morphology measurement of the thermopile is implemented to evaluate the influence of residual stress and practically characterize the geometric shape of the membrane. More careful analysis of the surface morphology shows that the bending of suspension parts has a deviation of responsivity of less than 0.167%. In this paper, the T-shape structure of the thermopile with large absorption area and high performance by using a CMOS-compatible process is proven to be very successful and is easily fabricated.

Investigation of thermal type microsensor with infrared photonic crystal

In this paper we have proposed a new complementary metal-oxide-semiconductor (CMOS) thermopile by leading the infrared photonic crystal (IPC) to increase the absorption of infrared radiation. A highly sensitive infrared detector requires an excellent signal induced by incident IR radiation to maximize the temperature change. A photonic crystal structure offers significantly effects of optical performance, especially for the absorption and emitting of radiation. Firstly we develop such a structure of thermopile with high performance by using 0.35µm 2P4M CMOS IC compatible process which can be easily and exactly fabricated. Several designs of infrared microsensors are proposed to study influential parameters from the photonic crystal structure. The measurement results show these devices get greatly responses higher than the thermopile without infrared photonic crystal. To that end, the investigation of field of view for our proposed thermopile is acquired, and the results show no significant difference between the thermopiles with or without PC. Our design is proved to be adequate for commercial batch production.

A New Approach of 2D CMOS Thermal-Bubble-Based Accelerometer

A novel thermal-bubble-based micromachined accelerometer with advantages of low solid thermal conductance and high sensitivity is presented in this paper. With our proposed micro-link structure, a new accelerometer was built with a micro heater, two pairs of thermopiles which were floating over an etched cavity. The micro-heater is centered on the membrane and two pairs of thermopiles besides are crossed with each other. The heater and the thermopiles are connected by network structure of micro-links, which enhance the structure and greatly reduce the solid heat flow from the heater to the hot junctions of thermopiles. Furthermore, the samples are fabricated by TSMC 0.35 mum 2P4M CMOS process which is provided by CIC with outstanding strong structures and uniform quality. Our design is proved to be adequate for commercial batch production.

Surface Morphology Measurement and Investigation of A New CMOS Compatible Thermopile with High Fill Factor

A new CMOS compatible thermopile was designed and fabricated with high fill factor, the floating membrane of the thermopile which we designed was formed by T-shape anisotropic etching window that never be proposed before. The design and fabrication of thermopile sensors are realized by using 1.2 mum CMOS IC technology combined with a subsequent anisotropic front-side etching. Four etching windows with minimum T-shape were opened by the CMOS processes, and then by using N 2H4 etching solution the silicon substrate was etched along <100> directions. The T-shape etching windows which proposed in this paper are designed at four quadrant of membrane to form the extended undercut etching area of opened windows of overlap. The floating membrane has a larger area of 1100 times 1100 mum2 and 2 mum thick. Therefore, the area of proposed membrane is increased greatly which absorbs more infrared radiation than the conventional design and enhances responsivity very well. A surface morphology measurement of thermopile is implemented to evaluate the influence of residual stress and characterize geometric shape of membrane practically. More careful analysis of surface morphology show the bending of suspension parts has a deviation of responsivity less than 0.167%. For our work, the T-shape structure of thermopile with large absorption area and high performance by using CMOS compatible process is proven to be very successful and easy fabricated

A CMOS compatible active thermopile with high frequency measurement

A considerable number of measurements for microsensors and system characterisations rely on the analysis of its step response. Device parameters of thermal microsensors are essential for evaluating the sensor performances and their simulation modelling. For the thermal microsensors, the thermal parameters are sometimes show important relations to the package, which is not an ideal heat sink. By decoupling the heat equations for the membrane of sensor and package, we first build a multiple-time-constant modelling of thermal microsensors, which describes a more realistic thermal behaviour. The behaviour on spectrum domain and time domain are predicted and been proved by our experiments. An investigation of high frequency response for CMOS compatible thermoelectric infrared sensors is proposed and fabricated. The sensors are fabricated by a 1.2 /spl mu/m industrial CMOS IC technologies combined with a subsequent anisotropic front-side etching stop. To reach a larger response signal, we fabricated a large floating membrane structure with a built-in polysilicon resistor as a signal modulator. It consists of a heating polysilicon resistor and an Al/ n-polysilicon thermopile, embedded in an oxide/nitride membrane. High frequency response of a test sample shows unexpected large signal, which is quite interesting and never reported before. We have made a thoroughly measurement and analysis, and give some interesting results.