AC Signal Characterization for Optimization of a CMOS Single Electron Pump
Roy E. Murray, Justin K. Perron, Michael D. Stewart, Neil M. Zimmerman
Pumping single electrons at a set rate is being widely pursued as an electrical current standard. Much work has been done on pumping using a single AC signal, but using multiple coordinated AC signals may help lower error rates. Whether pumping with one or two AC signals, it is important to know the properties of the AC signal at the device. In this work, we pumped electrons using a 2-gate ratchet style measurement and use the results to characterize and optimize our two AC signals. Fitting this data at various frequencies revealed both a difference in signal path length and attenuation between our two AC lines. We extracted the attenuation on the AC lines going to the device, plotting out the transfer function of each AC signal line. Using this data, we corrected for the difference in signal path length and attenuation by applying an offset in both the phase and the amplitude at the signal generator. We then switched to a 2-gate turnstile measurement to test the optimization parameters. Operating the device with the parameters determined from the 2-gate ratchet measurement led to much flatter, more robust charge pumping plateaus. This method was useful in tuning our device up for optimal charge pumping, and may prove useful to the semiconductor quantum dot community to determine signal attenuation and path differences at the device.