Copper atomic-scale transistors

Abstract

We investigated copper as a working material for metallic atomic-scale transistors and confirmed that copper atomic-scale transistors can be fabricated and operated electrochemically in a copper electrolyte (CuSO₄ + H₂SO₄) in bi-distilled water under ambient conditions with three microelectrodes (source, drain and gate). The electrochemical switching-on potential of the atomic-scale transistor is below 350 mV, and the switching-off potential is between 0 and -170 mV. The switching-on current is above 1 μA, which is compatible with semiconductor transistor devices. Both sign and amplitude of the voltage applied across the source and drain electrodes (U_bias) influence the switching rate of the transistor and the copper deposition on the electrodes, and correspondingly shift the electrochemical operation potential. The copper atomic-scale transistors can be switched using a function generator without a computer-controlled feedback switching mechanism. The copper atomic-scale transistors, with only one or two atoms at the narrowest constriction, were realized to switch between 0 and 1G₀ (G₀ = 2e²/h; with e being the electron charge, and h being Planck's constant) or 2G₀ by the function generator. The switching rate can reach up to 10 Hz. The copper atomic-scale transistor demonstrates volatile/non-volatile dual functionalities. Such an optimal merging of the logic with memory may open a perspective for processor-in-memory and logic-in-memory architectures, using copper as an alternative working material besides silver for fully metallic atomic-scale transistors.

Keywords: electrochemistry; encapsulation; metallic atomic-scale transistor; nanotechnology; photolithography.

Figure 1

Copper atomic-scale transistor. (a) Confocal optical microscopy image of the microelectrodes, electrolyte channel and the copper point contact (indicated with a dotted circle), which was deposited between the source and the drain. (b) Schematic diagram of an atomic-scale transistor.

Figure 2

The performance of copper atomic-scale transistors. (a) 0–1G₀ quantum conductance switching at 0.5 Hz. (b) 0–5G₀ quantum conductance switching at 1.5 Hz.

Figure 3

Controlled bistable quantum conductance switching of copper atomic-scale transistors. (a) 0–10G₀ switching at 0.57 Hz, U_G: −40 mV/210 mV (off/on). (b) 0–11G₀ switching at 0.73 Hz, U_G: −60 mV/120 mV. (c) 0–12G₀ switching at 0.89 Hz, U_G: −80 mV/140 mV. (d) 0–13G₀ switching at 0.33 Hz, U_G: −80 mV/240 mV.

Figure 4

Observation of fabrication and operation of the copper atomic-scale transistor. Confocal microscopy images taken before electrochemical copper deposition, after deposition, and during transistor operation are shown (from left to right).

Figure 5

The operation of a copper atomic-scale transistor driven by a function generator. (a) Schematic diagram of the function-generator-driven copper atomic-scale transistor connected to a current-to-voltage converter circuit. (b) Rectangular wave signal from the function generator (blue) switched between 0 and 300 mV with frequencies from 0.5 Hz to 4 Hz. The output U_out (red), following the signal from the function generator, is driven between 0 and −10.6 V. (c) Zoom-in on the switching sequence from 95 to 100 s.

Figure 6

Demonstration of bistable quantum conductance switching of the copper atomic-scale transistor driven with a function generator. The bistable quantum conductance switching (red) between 0–1G₀ (a) and 0–2G₀ (b) follow the controlling rectangular wave (blue) at 4 Hz between −105 mV (off) and 275 mV (on) given by the function generator.

Figure 7

Influence of the copper electrolyte additives on the morphology of deposited copper film. (a) Confocal optical microscopy image of the copper atomic-scale transistor taken in situ. (b) The switching performance of the transistor implemented with a rectangular wave signal from a function generator applied to the gate at 10 Hz is plotted in the upper graph (blue). The output signal U_out is in the lower graph (red). The sampling rate of the recording software is 50 samples/s. The solid circles are the measured data and the lines are guides to the eye.