Complementary Internal Ion-Gated Organic Electrochemical Transistors (C-IGT)

To understand and modulate neural network processes, bioelectronic devices capable of forming physiologically safe circuits to capture, amplify, process, and stimulate neural activity are required. Because signals of communication between neurons can be read out from minute changes in the ionic flux within brain tissue, organic mixed-conducting-based transistors that transduce ions to electrons can most effectively convert physiological signals to those suitable for input to electronics. These transistors can be fabricated to form conformable systems using scalable microfabrication processes to enable complex computational functions. Because most integrated circuits are currently designed based on complementary transistors (N and P-type), development of the combination of equal performance N and P-type IGTs would permit seamless integration with pre-existing designs. Here we demonstrate a method to create transistors with N-type function, transistor action in the first quadrant and resistor like in the third quadrant, from P-type materials which usually express the opposite behavior, modulating in the third quadrant and acting as a resistor in the first quadrant. These opposing behaviors enabled a complementary logic device with an output voltage range similar to the input voltage dynamics. Additionally, similar channel material and geometry resulted in equal impedances between the two transistors yielding a higher power efficiency. To accomplish this, we created geometrically asymmetric transistor design for optimal complementary performance. An array of devices with different source, gate, and drain sizes were analyzed to determine design rules N and P type performance. Channel material additives were evaluated to find the best formula for creation of both types of transistor for use in complementary devices. Transistors were characterized in terms of asymmetry, voltage required for complementary operation, speed, and gain. Using designs informed by the characterization of channel asymmetry we then fabricated all logic gates to demonstrate digital operations. These complementary IGT designs which can be fabricated with both N and P type single channel materials have a broad range of applications in bioelectronics including wearable electronics, neural interfacing, and therapeutic implants.