Electron pumps are typically fabricated using lithographic masks defined by electron beams. This process has the high resolution and flexibility required to fabricate prototype single electron devices in Si or GaAs systems, but is relatively slow and not compatible with techniques used for larger scale production of devices, or for integration into a larger device architecture. e-SI-Amp partners CEA have demonstrated that working electron pumps based on silicon nanowires can be fabricated using industry-standard deep-UV optical lithography on 300 mm wafers.

Top: Schematic of single electron island defined in a silicon nanowire. Bottom: TEM of gate structure with scale bar.

The pump devices are based on patterning silicon nanowires with two surface gates which confine a central quantum dot region. Details of the fabrication process can be found in the paper. Single dot Coulomb blockade conditions can be achieved for the correct back gate voltage. Adding appropriately phase-shifted control ac voltages to the gate bias voltages can move electrons onto and off the central island giving a quantized pump current.

The device performance is shown to be comparable to that of electron-beam defined devices and shows quantized pumping up to frequencies as high as 300 MHz.

In real devices, additional transport processes are possible due to impurities under the control gates. This can actually reverse the polarity of the pump current under certain conditions.  The authors show a model of this behaviour which matches experimental data.

The exploration of alternative fabrication schemes may be important for parallelisation of electron pump operation (to increase pumped current) using many pumps.

Design and Operation of CMOS-Compatible Electron Pumps Fabricated With Optical Lithography 
P. Clapera, J. Klochan, R. Lavieville, S. Barraud, L. Hutin, M. Sanquer, M. Vinet,
A. Cinins, G. Barinovs, V. Kashcheyevs, and X. Jehl
IEEE Electron Device Letters  38, 414 (2017);
doi: 10.1109/LED.2017.2670680

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