Chen-Hsun Du

Characterization of Thermopile Based on Complementary Metal-Oxide-Semiconductor (CMOS) Materials and Post CMOS Micromachining

In this paper we present the characterization of a practical thermopile sensor, using extensive experimental results of measurement of heat conductance of thermopile produced by a complementary metal-oxide-semiconductor (CMOS) compatible process and front-side Si bulk etching. Several parameters, such as width of polysilicon, length of thermopile, number of thermocouples, overlap length of hot junction on absorber and area of absorption layer, are investigated. We also use a heater on the central membrane in order to heat the membrane. Both the power source from a blackbody IR source and the heater on the membrane are selected to heat the membrane. The device properties in vacuum and in the atmosphere were measured in order to distinguish the effect of heat conductance due to gas convection. In this study, the thermal characterization of the thermopile sensor is conducted. A model is established to predict the properities of device with some geometric and process-related factors are coupled.

Investigation of TMAH for front-side bulk micromachining process from manufacturing aspect

Abstract An investigation on the influence of etchant concentration, dissolving silicon content and additives during silicon anisotropic etching in tetramethyl ammonium hydroxide (TMAH) has been carried out. Based on the Taguchi method, the etch rates of Si, Al, and SiO 2 were measured via under-etch experiments using the wagon-wheel mask pattern. The improvement on the surface quality was observed by agitating the solution under ultrasonic vibration in TMAH solutions with additives. Furthermore, a new approach is developed to reduce wet etching time and to control etched gap depth between the released micromembrane and the silicon substrate. This method employs a polysilicon or an amorphous silicon thin layer embedded between the micromembrane and silicon substrate as a sacrificial layer, then this layer would be fast isotropically etched away by TMAH solution.

Optimization criteria of CMOS-compatible thermopile sensors

This paper presents an extensive review of optimization criteria of thermopile detector. The heat conductance and resistance of thermopile structure, the thermal-electric coefficient of thermocouple, and area of absorption layer are critical to the performance of thermopile. As a result, the critical features like responsivity and detectivity are widely considered and incorporated into a mathematical model in terms of the parameters like sheet resistance and width of polysilicon, length and number of thermocouple, area of radiation absorber, and geometric structures. The effect and correlation of these parameters are evaluated through this way. The design rule of CMOS compatible thermopile sensor is developed based on simulated conclusions. The optimized thermopile structures with responsivity higher than 100V/W, and specific detectivity better than 1 X 108cm(root)Hz/W can be derived. Finally, optimization criteria of thermopile detector is verified and discussed.

Investigation of thermopile using CMOS compatible process and front-side Si bulk etching

This paper presents an extensive experiment results of measuring properties of thermopile detector produced by CMOS compatible process and front-side Si bulk etching. The thermoelectric materials used are n- polysilicon and aluminum. Several parameters of thermopile detectors, such as width of polysilicon, length of thermopile, number of thermocouple, overlap length of hot junction into absorber area, and area of absorption layer are investigated in this study. Any physical characteristics of thermopile detectors, such as responsivity and detectivity of each device are measured as well. The heat conductance, resistance of thermopile structure, and the thermal-electric coefficient of thermocouple are critical to the performance of thermopile. All of them will affect the characters of sensor. In general case, a trade-off relation is among these parameters. When we design thermopile devices, we must consider these issue and determine a set of optimized parameters. In our investigation, the relation of each parameter and the device characters are measured. And the effect and correlation of these parameters versus thermopile property are evaluated. Based on these experiment results we can know the operation mechanism and correlation effect of these parameters. Establishment of accurate model for thermopile helps us to design an optimized device for various applications.

3D thermoelectric structures derived from a new mixed micromachining process

This paper presents an innovative two-level thermoelectric structure which significantly reduce the component size without deterioration of sensor performance. Based on CMOS compatible process, this two-level thermoelectric structure is demonstrated and fabricated by combining front-side silicon anisotropic wet etching and aluminum sacrificial layer etching technique. The voltage responsivity of derived thermopile with 300/spl times/300 /spl mu/m/sup 2/ pixel size can be as high as 162 V/W in vacuum. This new thermoelectric structure shows its potential to be an excellent pixel structure of infrared sensor array for security application.

Characterization of thermopile based on CMOS materials and post CMOS micromachining

Recently, the micromachined sensors using CMOS compatible process are developed and attractive for mass production. The thermopile sensor manufacture by CMOS process and post-CMOS bulk micromachining was reported by H. Baltes (2000), that using back-side Si bulk etching using KOH solution. This paper presents characterization analysis of practical thermopile sensor, using the extensive experiment result of measuring heat conductance of thermopile detector produced by CMOS compatible process and post front-side Si bulk etching using TMAH solution.

Development of TMAH anisotropic etching manufacturing process for MEMS

An investigation on the influence of etchant concentration, dissolving silicon content and additives during silicon anisotropic etching in TMAH has been carried out. Based on the Taguchi method, the etch rates of Si, Al, and SiO2 were measured via under-etch experiments using the wagon- wheel mask pattern. The improvement on the surface quality was observed by agitating solution under ultrasonic vibration in TMAH solutions with additives. Furthermore, a new approach is developed to reduce wet etching time and to control etched gap depth between the released micro membrane and the silicon substrate. This method employs a polysilicon or an amorphous silicon thin layer embedded between the micro membrane and silicon substrate as a sacrificial layer, then this layer would be fast iso tropically etched away by TMAH solution.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.