A printed gate controlled electrochemical capacitor-diode (G-CAPode) for AC filtering applications

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-depended 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 current and voltage output of the W-Cap depending on the applied gate bias between 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 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.