Unpowered event detection with an autonomous ferroelectric capacitor circuit

The availability of discrete ferroelectric capacitors opens the possibility of unusual sensors capable of detecting events while the sensor circuits are unpowered. The simplest method utilizes the classic Sawyer-Tower circuit in conjunction with a microprocessor. A more sophisticated approach that eliminates the need for a microprocessor takes advantage of the unique characteristics of the autonomous ferroelectric memory latch. The core operation is for the ferroelectric capacitor of the detection circuit to be set to a known state after which the circuit is powered down. An event detector or sensor that generates its own electrical energy switches the ferroelectric capacitor to the opposite state upon the occurrence of an event even though the sensor circuit is powered down. The state of the capacitor is read after the circuit is re-powered to determine if an event occurred while the circuit slept. The author will provide a short history of non-volatile ferroelectric memory and then explain the basic operation of such an unpowered event detector along with the circuits that may be used to implement such a detector.