Non-Volatile Doping of Graphene Transistors using a Solid Polymer Electrolyte Crosslinked by Field Effect for Polymorphic Electronics

Hardware security comes at a high price in the U.S. at $200 billion annually. Polymorphic electronics provide a potential solution to hardware security threats by preventing unauthorized parties from accessing circuitry information through reverse engineering. The goal of this work is to obscure a device’s function by taking advantage of electric double layer (EDL) gating to reconfigure NAND gates to/from NOR gates on-demand. The key innovation is a custom-synthesized polymer electrolyte that reacts under an electric field created by the EDL (~V/nm), retaining charges in the channel by crosslinking the polymer electrolyte. Ion mobility is confirmed in a lateral, parallel-plate capacitor geometry, and graphene field effect transistors (GFETs) are used to test non-volatile doping. Preliminary evidence of non-volatile doping is observed by programming GFETs at positive gate voltages (V_G > +2 V), and then sensing the Dirac point shift and ON/OFF ratio change. Positive programming voltages less than +2 V showed no effect on the doping; however, the device becomes more n-type, and ON/OFF increases as V_G increases from +2 to +5 V. Note that in the absence of a non-volatile doping mechanism, grounding the gate would dissipate the EDL and reverse the doping effect; however, in the case of our custom synthesized electrolyte, the doping effect persists even after the gate bias is grounded, confirming non-volatile doping at the graphene channel. Applying a negative V_G demonstrates a semi-permanent - but reversible - doping effect. Specifically, as V_G increases from -1 to -5 V, the Dirac point shifts less n-type and ON/OFF decreases, implying that the doping effect is reversible but non-volatile. We will also report on the sheet carrier densities measured by Hall effect to quantify the doping, along with chemical characterization of the polymer electrolyte. The work is supported by the National Science Foundation (NSF, U.S.) under Grant No. ECCS-EPMD-2132006