Thermo-mechanical characterization of micromachined GaAs-based thermal converter using contactless optical methods

Design and construction of GaAs-based micromachined thermal converter device consisting of a high electron mobility transistor (as a microwave heater) and a thin film resistor (as a temperature sensor), integrated on 1 μm thick polyimide fixed GaAs/AlGaAs island structure are introduced. The influence of thermal residual stresses as well as device temperature variations on membrane-like multilayer structure are discussed. A noninvasive and contactless optical methods such as laser confocal microscopy, laser Doppler vibrometry (LDV) and thin layer interferometry are applied to analyze experimentally the thermo-mechanical properties of the micromachined device. LDV method is used to evaluate the device temperature time constant (τc ∼1.5 ms) and nano-deformations induced by the temperature changes at any point of device. A confocal microscope is chosen to analyse the 3D deformation profiles of the device at different temperature-induced stress states. The device deformation changes (∼3 μm) induced by power dissipation of 9.5 mW (temperature increase of 395 K) are found to be negligible with respect to the dimensions of the polyimide fixed island structure (160 μm × 120 μm).The optical characterization methods are proved to be a useful tool in design of new thermally based MEMS devices.