A Printed Gate Controlled Electrochemical Capacitor‐Diode (G‐CAPode) for AC Filtering Applications

ABSTRACT For the first time, a printable, miniaturized, and gate‐controlled electrochemical capacitor‐diode (G‐CAPode) is presented. The heart of the device consists of a recently developed asymmetric electrical double‐layer capacitor system based on selective, size‐dependent ion adsorption. Due to the introduction of a sieving carbon with ultramicroporous pores ( d = 0.69 nm) as one electrode material, an effective blocking of ions with sizes below the pore size of the carbon can be achieved, leading to a unidirectional charging comparable to a diode (CAPode). This “working capacitor” (W‐Cap) was further expanded by introducing a third (“gate”) electrode enabling a control of the current and voltage output of the W‐Cap depending on the applied gate bias between the gate electrode and counter electrode of the W‐Cap resembling transistor features. By varying the gate bias voltage, the potentials and therefore the working window of the W‐Cap electrodes are shifted to more positive or negative potentials, leading to an increase or decrease of the G‐CAPode capacitance. The printed G‐CAPode was tested as a switchable device analogous to an I‐MOS varactor for the adjustable filtering of AC signals in a high‐pass filter and band‐pass filter application. This investigation opens the possibility to couple capacitive (energy storage), diodic (current rectification), and transistor (voltage‐controlled switching) characteristics in one device and also addresses its process integration via 3D printing.