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Reduction of Inhomogeneous Elastic Strains in Devices such as Josephson Junctions

IP.com Disclosure Number: IPCOM000089605D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 22K

Publishing Venue

IBM

Related People

Matthews, JW: AUTHOR [+2]

Abstract

A system consisting of an oxide layer on a metal substrate on a silicon backing deforms inhomogeneously when its temperature is changed. This deformation, even for relatively small temperature changes and plastically strong materials, is not entirely elastic, as can be demonstrated by the hysteresis loop of measurements of the material lattice parameters during a temperature charge cycle.

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Reduction of Inhomogeneous Elastic Strains in Devices such as Josephson Junctions

A system consisting of an oxide layer on a metal substrate on a silicon backing deforms inhomogeneously when its temperature is changed. This deformation, even for relatively small temperature changes and plastically strong materials, is not entirely elastic, as can be demonstrated by the hysteresis loop of measurements of the material lattice parameters during a temperature charge cycle.

Inhomogeneity in both the elastic and plastic deformation gives rise to stress concentrations (for example, see references [1-3]). That can cause failure of a device by the cracking and resultant shorting of the oxide layer and by the failure of contacts on the superconducting region. Thus, it is desirable to reduce the degree of inhomogeneity of the internal strain fields as far as possible. Any such reduction will lead to improved life time of the device.

Here, we describe a technique by means of which stress concentrations resulting from inhomogeneous deformation can be reduced and device life time thereby increased.

(1) In changing the temperature of a fabricated device from T(1) to T(2) a procedure should be adopted in a cyclically staged manner as indicated diagramatically below.

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The reverse temperature changes of the type b --> c should be between 1/3 and 1/2 of the temperature changes of type a --> b. This approach should be used in both generally raising and lowering the device temperature and in all temperature cycling. The reason why this approach should give a reduction in the inhomogeneity of the elastic strains at any temperature is as follows: Any plastic deformation of an inhomogeneous type, in, for example, the stage a --> b, gives rise to an inhomogeneous stress field, which is removed more rapidly by reverse deformation for example, see reference [3]). The module a --> b --> c need not be of the same magnitude throughout an overall temperature change, but should be reduced in range over any given temperature change whether in raising or lowering the device temperature overall.

(2) To further reduce the deleterious effects of inhomogeneous plastic deformation, the temporal rate of any tempera...