Tham khảo tài liệu 'micromachining techniques for fabrication of micro and nano structures part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Modeling and Simulation of MEMS Components Challenges and Possible Solutions 289 Fig. 3. The structure of the power sensor. left-hand top view right-hand-side sectional view along A-A . Step 1 Description of the Physical Problem A sectional view of the configuration of the sensor to be modeled is depicted in Fig. 3. The sensor is composed of a thermally isolated thin 2 pm AsGaAs GaAs membrane region with a terminating resistor in which heat generated by DC or RF power is dissipated and converted into heat. A high-thermally resistive membrane region is obtained by selective etching of the GaAs against AlGaAs. This helps to increase temperature gradient between the resistor region and the rest of the chip thus leading to high sensitivity. Temperature increase in the resistor region is sensed by a set of Gs Au-Cr thermoelements whose dc output is proportional to the input RF power. Detailed description of technical realization of this sensor is given by Mutamba et al. 2001 . Steps 2 3 The Governing Equations and Approximations Here we consider both the thermal and the electric models. The mathematical model is required to be simple enough to be handled by known methods which demand reasonable time and cost and at the same time give an adequate description of the physical problem under investigation. Thermal model A simplified pictorial view of the sensor is shown in Fig. 3 for the purpose of thermal modeling. Here the thermocouple wires are not shown and heat generated by the NiCr resistor is assumed to be distributed throughout the sensor structure mainly by conduction. Due to axial symmetry of the sensor structure about it longitudinal axis we only consider half of its geometry as shown in . We select Cartesian coordinates x y z with its origin at the sensor input and the direction of power transmission along the positive z-direction. In order to obtain a simple and manageable model the following simplifying assumptions are made i. The presence of the .
