Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Fabrication of Josephson Tunneling Barriers

IP.com Disclosure Number: IPCOM000050921D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Broom, RF: AUTHOR [+4]

Abstract

In Josephson tunneling devices, fabrication of the tunnel barrier is an important step. If the tunnel barriers of all devices are uniform in their composition and thickness, the device characteristics of all the tunnel junctions in an array will be the same. Since the tunnel barrier is generally very thin (on the order of 20-50 angstroms), it is often difficult to provide reproducibility of the barrier fabrication process, especially if different base electrode materials are used. The processes described in this article combine sputtering and oxidation in an oxygen plasma in order to accomplish this.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 2

Fabrication of Josephson Tunneling Barriers

In Josephson tunneling devices, fabrication of the tunnel barrier is an important step. If the tunnel barriers of all devices are uniform in their composition and thickness, the device characteristics of all the tunnel junctions in an array will be the same. Since the tunnel barrier is generally very thin (on the order of 20-50 angstroms), it is often difficult to provide reproducibility of the barrier fabrication process, especially if different base electrode materials are used. The processes described in this article combine sputtering and oxidation in an oxygen plasma in order to accomplish this.

In the case of alloy electrodes, such as lead-based alloys, parameters that are intrinsic as well as extrinsic to the electrodes must be be controlled. Often, the alloy electrodes have undergone ambient, chemical, and thermal exposure before barrier formation begins. An example is a Josephson tunneling device using an InAuPb alloy for the base electrode, on which the tunnel barrier is to be formed, a native oxide for the tunnel barrier, and a PbAu alloy for the counterelectrode. The tunnel barrier is formed by RF oxidation through a stencil prior to counterelectrode deposition. Although oxidation in an RF plasma is a reproducible process if parameters such as pressure, temperature, and ion energy are controlled, the use of alloy electrodes and the presence of the stencil and other contaminants as a result of ambient exposure require further control.

A four-step process that is suitable for fabrication of the tunnel barriers on these alloy electrodes is as follows: 1. With the samples shuttered, a high power, low pressure RF

oxidation discharge is used to clean the vacuum chamber

and the RF cathode which has had ambient exposure.

2. With the samples now exposed, a low power, high pressure

RF oxidation discharge is used to clean photoresist and

other residues from the stencil.

3. RF oxidation at fixed oxygen pressure, cathode voltage,

temperature, O(2) gas flow, and discharge time is then

utilized to fabricate the tunnel barrier.

4. The counterelectrode is then deposited. A high degree of

control of the temperature, flow, oxygen pressure, and

cathode voltage is maintained during the entire oxygen

process.

These general techniques can also be used if the electrode materials are different from the Pb-based alloys described above. For example, the technique can be applied to the fabrication of niobium-niobium oxide Josephson junctions. However, consideration must be given to the following initial conditions wh...