Design And Simulation Of The Structure For On-Line Determination Of Thermal Expansion Coefficient Of Polysilicon Thin Films

The dimension of MEMS devices ranges from several microns to a few hundred microns. The mechanical properties of micro-machined devices depend not only on the material used, but also on the size and the shape of the microelement. Hence, special test structures should be designed to achieve the characteristics of microstructures with different sizes and shapes. In this paper, we present two test structures for on-line determining the thermal expansion coefficient (TEC) of thin films.The key rules for the design of an on-line test structure for determining TEC of thin films mainly rely on these points as follows. 1. The processes for the test structure and the materials to be tested should be identical and no special processes for the test structure are permitted. 2 The test structure should be able to provide compatible electrical output interface for post data disposal modules. 3. The structure should be as easy as possible and its calculation model should be able to reflect the actual situation of the test structure under the precondition that the accuracy can be assured. 4. The requirements for the test circumstance and equipments can not be too high. There are already several test structures, based on MEMS technologies, utilized for the measurement of TECs of MEMS thin films, however, they can not meet all the requirements mentioned above. In this paper, two test structures, based on bent beam and cascaded bent beam structures, and their analytical models are introduced. The thermal-electrical-mechanical compliant model for the cascaded bent beam structure has been put forward for the first time, which will contribute a lot to the design and analysis of both test structures and thermal cascaded bent beam actuators. Furthermore, some optimizations for the design of test structures have also been presented based on these two analytical models.