A CMOS compatible GHz ultrasonic pulse phase shift based temperature sensor

This paper presents an ultrafast and high-resolution temperature sensor utilizing the phase shift between the transmitted and received ultrasonic pulses through silicon substrate. The ultrasonic pulses are generated using piezoelectric AlN thin film transducers fabricated on top of a silicon wafer. The generated ultrasonic pulse packet propagates through the silicon thickness, reflects from the wafer back side and is sensed at the top side. The ultrasonic pulse undergoes multiple reflections in the silicon substrate creating multiple echoes. Due to both the thermal expansion coefficient of silicon and the speed of sound in silicon temperature coefficient, the phase shift between the transmitted signal and the received echoes increase as temperature of the substrate increases. The temperature coefficient of phase shifts multiplies as the echo order increases. Second and third echoes have double and triple the temperature coefficient as the first echo. By detecting the phase shift of the multiple echoes, wide dynamic range, high resolution and scale-factor repeatability can be achieved simultaneously. The sensor demonstrates high linearity with a phase-shift temperature coefficient of 12°/°C across a temperature range of 30-120°C, with 17 m
^°
C resolution at 6μs sampling times.