memcapacitor

A memcapacitor is a passive two-terminal memory circuit element whose capacitance depends on the past history of voltage or charge. In a memcapacitor, the relationship between charge and terminal voltage is not fixed but is modulated by an internal state that encodes information about previous signals. The constitutive relation is usually written as q = C(x, V, t) · V, where C is a state-dependent capacitance and x is an internal state vector evolving according to dx/dt = f(x, V, t). This allows the capacitance to change in response to voltage, current, or time, producing memory effects and hysteresis in the device's C–V or Q–V characteristics.

Physical implementations are often realized in systems where an internal degree of freedom—such as ionic positions, polarization in ferroelectrics, or mechanical displacement—remembers past stimuli. Common realizations include ferroelectric capacitors, ion-conducting or electrochemical structures, phase-change materials, and micro-electro-mechanical systems.

Memcapacitors are studied for non-volatile memory and neuromorphic computing, where adaptive or programmable capacitance can be used for memory storage, synaptic-like weighting, or reconfigurable analog circuitry. They are part of a broader family of memory circuit elements that also includes memristors and meminductors, sharing a dependence on the history of electrical signals.

Despite interest, practical deployment faces challenges such as device variability, retention, and modeling complexity; nonetheless, memcapacitive concepts continue to influence research in adaptive electronics and memory devices.