Process and Device Simulation of SAW Temperature Sensors Compatible with 1 µm CMOS Technology

Abstract

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.