Towards a CMOS compatible ultrasonic delay line memory

In this paper, we present the concept and demonstrate the use of recirculating ultrasonic pulses as memory elements, stored in the thickness of a silicon wafer. This memory can be called SIUM, Substrate Integrated Ultrasonic Memory, and can be integrated within CMOS. We outline a theory of maximum SIUM spatial density. In this paper, we demonstrate a 2 bit delay line memory with the bulk of the silicon wafer as the delay line medium, using high frequency, thin film aluminum nitride (AlN) transducers. Pulse lengths of 16 ns was used at a carrier frequency of 1.3 GHz, at 2.1 volts peak to peak applied to the AlN films. These voltages and frequency ranges can be implemented in silicon CMOS for complete integration within an integrated circuit.