Using granular film to suppress charge leakage in a single-electron latch

Alexei O. Orlov, Xiangning Luo, Kameshwar K. Yadavalli, I. S. Beloborodov, and Gregory L. Snider

Phys. Rev. B 77, 075414 – Published 15 February 2008

Abstract

A single-electron latch is a device that can be used as a building block for quantum-dot cellular automata circuits. It consists of three nanoscale metal “dots” connected in series by tunnel junctions; charging of the dots is controlled by three electrostatic gates. One very important feature of a single-electron latch is its ability to store (“latch”) information represented by the location of a single electron within the three dots. To obtain latching, the undesirable leakage of charge during the retention time must be suppressed. Previously, to achieve this goal, multiple tunnel junctions were used to connect the three dots. However, this method of charge leakage suppression requires an additional compensation of the background charges affecting each parasitic dot in the array of junctions. We report a single-electron latch where a granular metal film is used to fabricate the middle dot in the latch which concurrently acts as a charge leakage suppressor. This latch has no parasitic dots, therefore the background charge compensation procedure is greatly simplified. We discuss the origins of charge leakage suppression and possible applications of granular metal dots for various single-electron circuits.

Received 8 September 2007

DOI:https://doi.org/10.1103/PhysRevB.77.075414

Authors & Affiliations

Alexei O. Orlov¹, Xiangning Luo¹, Kameshwar K. Yadavalli^1,2, I. S. Beloborodov^3,4, and Gregory L. Snider¹

¹Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
²Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA
³Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁴James Franck Institute,University of Chicago, IL 60637, USA

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Vol. 77, Iss. 7 — 15 February 2008

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Images

Figure 1
(a) A four dot QCA cell. Two diagonal electron configurations represent two possible binary states. (b) Functional scheme of a clocked QCA cell based on single-electron latches. Single-electron latch is outlined by a dashed box. $E_{1}$ is a SET electrometer to read out the cell polarization.Reuse & Permissions
Figure 2
Sketches of single-electron devices employing granular metal islands. Aluminum (Al) with thin oxide on top is shown in gray, white bars represent $Cr O_{x}$ film deposited on top of Al. (a) Single-electron latch. Middle dot $D_{2}$ is made of granular metal. Differential input signals ( $+ V_{IN}$ and $V_{IN}$ ), clock signal $(V_{CLK})$ , and electrometers ( $E_{1}$ and $E_{2}$ ) are capacitively coupled to $D_{1}$ , $D_{2}$ , and $D_{3}$ as shown in the figure. Electrometers $E_{1}$ and $E_{2}$ are fabricated in the second step of e-beam lithography. (b) Single-electron transistor with granular metal $(Cr O_{x})$ island. Source and drain leads, and the gate, are shown.Reuse & Permissions
Figure 3
Phase plots of single-electron latches: [(a) and (b)] Single-electron latch with $Cr O_{x}$ middle dot. Dot potential (of $D_{1}$ ) is measured by electrometer $E_{1}$ for two directions of the differential input signal as shown by the arrows ( $X$ axis is the same for both directions of the input voltage). Triangularly shaped areas outlined with dashed lines indicate bistable behavior. (c) An $Al ∕ Al O_{x}$ latch with the same design (two junctions). Only one plot is shown because plots for the opposite directions of the scans are indistinguishable in this case. No bistability is seen in this plot.Reuse & Permissions
Figure 4
Operation of the QCA latch with $Cr O_{x}$ middle dot: (a) applied input bias, (b) clock bias, and (c) potential of $D_{1}$ measured by electrometer $E_{1}$ . An instance of a leakage error is shown by the dashed line. (d) Leakage error probability for the latch in the hold state as a function of time elapsed from the moment the electron is latched. Cumulative leakage error probability is plotted for 192 scans as a function of time elapsed from the moment the differential input bias is removed $(t_{0}, t_{2})$ . The dashed line is a fit using formula (3) with parameter $τ = 1.05 s$ .Reuse & Permissions
Figure 5
Large scale phase plots of the two single-electron latches: (a) Latch with two $Al O_{x}$ junctions and $Cr O_{x}$ middle island. (b) An $Al ∕ Al O_{x}$ latch with six tunnel junctions (two branches connecting the middle dot to the end dots each have three junctions). Note that a distinct triangular pattern is clearly seen throughout the whole plot for the latch with $Cr O_{x}$ island, whereas it appears only on a small portion of the plot for the $Al ∕ Al O_{x}$ latch.Reuse & Permissions

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