In this paper, we investigate numerically the coupling of the Rayleigh mode with the micro-wall resonance modes in inter-digital transducers (IDTs) electrodes of surface acoustic wave (SAW) devices. We perform a finite element analysis (FEA) of the SAW features using an implemented model using COMSOL Multiphysics® software. The SAW structure comprises identical transmitter and receiver IDTs electrodes, with different electrode heights (he). The proposed FEA study is based on the extraction of reflection (S11) and transmission (S21) coefficients of the SAW device. The IDTs are considered to be a micro-wall phononic crystal acting as local resonators at frequencies inside the SAW passband. The locally resonance gap is strongly dependent on the he value, S11 and S21 parameters are affected by the SAW energy absorption in the IDTs system. We have chosen two he values (0.5 and 3 µm) to study low and high aspect ratios of micro-walls; corresponding respectively to Bragg-type and resonance-type bandgaps appearing near to the SAW central frequency. At the SAW resonance frequency, the return (S11) and the insertion (S21) losses are reduced. S21 is reduced by 12.73 and 18.49 dB for he=0.5 and 3 µm, respectively, accompanied by an increase in the quality factor, and S11 parameter is reduced by 1.357 and 4.98 dB for he=0.5 and 3 µm, respectively.
Process and device simulation of a surface acoustics wave (SAW) temperature sensor based AlN material as piezoelectric film, grown on Si wafer and patterned with Al electrodes, is described. CMOS 1 µm process is the process used to simulate a SAW sensor with number of IDT electrodes pairs Np = 16 using Silvaco software; fabrication steps inside the cleanroom are also described. The Athena Silvaco module is used for technological process simulation and the Atlas module is used to characterize the sensor in terms of electrical potential and electric field distribution under IDTs. IDS = f (VDS) simulation curves are compared to those issued from experimental characterizations performed on PMOS and NMOS transistors realized by 1 µm CMOS technology. The mask needed for SAW realization is designed. In order to choose the best sensor to manufacture, two SAW sensors with Np = 16 are characterized using Comsol multiphysics. Their IDTs length “a” and spacing “b” are 2 µm for the first sensor and 3 µm for the second one, which corresponds to 600 MHz and 400 MHz resonance frequencies respectively. The mechanical displacement field at the center frequency of the 3 µm structure and the reflection coefficients (S11) of both structures are determined to deduce the piezoelectric response. Afterwards, the SAW temperature sensors are studied in the temperature range extending from −25 °C to 200 °C; their sensitivities are evaluated at 19.10 ppm/°C and 23.53 ppm/°C for 600 MHz and 400 MHz devices respectively.
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