Results and model for single-gate ratchet charge pumping

Single-gate ratchet pumping is based on a Brownian motor mode, and thus can present subtle behavior. We show experimentally that, in the same devices, we can demonstrate multiple two-gate pumping modes but not the single-gate mode. We propose three mechanisms to explain the lack of plateaus in the single-gate ratchet mode: a large plunger-to-barrier ratio compared to the charging energy (Δptb/EC), nonlinear tunnel barriers, and phase offset leading to nonequilibrium heating. Our analysis shows that each of these could contribute to the lack of plateaus in the 1-gate ratchet pumping, but allow 2-gate pumping methods to work with robust plateaus. We propose several methods to reduce these sources of error, including reducing gate oxide thickness and reducing cross capacitances.