An adaptive ferroelectric transformer—A solid-state analog memory device

Abstract

A new solid-state adaptive (analog memory) device is described and demonstrated. The device is a flat-band electronic transformer with adaptable voltage gain; that is, the voltage gain-frequency transfer characteristic can be "set" to different values of attenuation by the application of an adapt signal and will retain that setting after the adapt signal has been removed. Ferroelectric materials are used as the dielectric in the transformer structure composed of two capacitors bonded together so that mechanical vibrations established in one (the input capacitor) are coupled to the other (the output capacitor). Converse and direct piezoelectric effects generate the mechanical vibrations and the output voltages, respectively. Ferroelectric effects in either capacitor provide the analog memory capabilities. Experimental adaptive transformers demonstrated are suitable for audio frequency operation. The voltage and current gain-frequency transfer characteristics are flat over the entire audio frequency range. Maximum gain is typically about -20 dB. Application of a voltage pulse (100 to 300 volts) of low energy (mJ) to either side of the transformer can adapt the gains to specific lower settings (between-20 and -60 dB) within an arbitrary switching time (roughly 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> seconds) as determined by the pulse amplitude. Gain settings are electrically stable to within a few percent of the maximum gain for periods of at least one year, and possibly indefinitely, and can be reproduced by the same or an equivalent sequence of adapting pulses.