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Metal Oxide Metal Devices with Contact Area Less Than 10/-11/cm/2/ for Josephson and Room Temperature Applications

IP.com Disclosure Number: IPCOM000052448D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 5 page(s) / 64K

Publishing Venue

IBM

Related People

Broers, AN: AUTHOR [+4]

Abstract

This article relates generally to metal oxide metal (MOM) devices which operate at liquid helium and room temperatures. More specifically it relates to such devices which have contact areas less than 10/-11/cm/2/ Two new device configurations and fabrication procedures which will enable the reduction of the effective area of tunneling in metal oxide metal devices (MOMs) to less than 10/-11/cm/2/ are disclosed.

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Metal Oxide Metal Devices with Contact Area Less Than 10/-11/cm/2/ for Josephson and Room Temperature Applications

This article relates generally to metal oxide metal (MOM) devices which operate at liquid helium and room temperatures. More specifically it relates to such devices which have contact areas less than 10/-11/cm/2/ Two new device configurations and fabrication procedures which will enable the reduction of the effective area of tunneling in metal oxide metal devices (MOMs) to less than 10/- 11/cm/2/ are disclosed.

Area Considerations in Normal MOMs: These devices have established themselves as the fastest classical mixers and detectors with an upper frequency limit in the 10/13/ Hz regime. The limiting factor is the RC time constant, where R is the dynamic resistance and C is the capacitance between the two parallel metal plates. Devices with R approx. over = 50 Omega have a time constant which is approximately proportional to the area. For areas of 10/-11/cm/2/, time constants in the range of 10/-11/ sec. are accessible.

Area Considerations in Josephson MOMs: Here, the time constant is the limiting factor in the device switching speed. Especially in Nb-Nb(2)0(3) junctions where the relative dielectric constant is close to 30, devices with large area are not tolerable [1].

Small area devices generally lead to denser circuitry and improved uniformity of oxide over the tunneling area. Moreover, from B purely scientific point of view, when areas are in the range of 10/-10/cm/2/ or so, the required oxide thickness for a selected current density is very thin, in the range of a monolayer or two.

"Edge MOM": "Edge MOMs" have previously been constructed [2,3,4]. The advantage of such devices is that they use standard optical lithography and tunneling areas in the range of 10/-10/cm/2/ are achieved. Fig. 1 shows an "Edge MOM" 1. The effective tunneling area is achieved by an overlap of a metal strip 2 (1 Mu wide) over an oxidized edge 3 of a thin Metal film 4 which is sputtered or evaporated and can be as Thin as 100 Angstrom.

This article shows how the device of Fig. 1 may be improved by reducing the width of the overlay strip 2 down to 100-300 Angstrom using the combination of Ni-Ni oxide - Ni for the normal MOM's and Nb-Nb oxide Nb for the Josephson MOMs.

In the following, the fabrication process which uses both

"contamination resist" to draw approx. 200 Angstrom lines and sputter-oxidation [5] to achieve approx./< 10 Angstrom oxide thickness is briefly described. The device (Fig. 2 fabricated on a silicon wafer 10 coated with a 1600 Angstrom layer 11 of Si(3)N( with a window 12 which is etched from the bottom to minimize the back scattering of secondary electrons in the process of writing the approx. 200 Ang lines. A cross-section through the final structure is shown in Fig. 2. A junction 13 is formed by the overlap of a thin metal film 14 over an oxide barrier 15 on the edge of metal 16.

A top view in Fig. 3 shows the shape...