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Phonon-Mediated Quasiparticle Injection Transistor

IP.com Disclosure Number: IPCOM000059916D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 6 page(s) / 31K

Publishing Venue

IBM

Related People

Epperlein, PW: AUTHOR

Abstract

Two superconducting tunnel junctions, separated by a thin dielectric layer for phonon transfer, form a three-terminal superconducting device which has good isolation characteristics. This article describes the use of superconducting tunnel junctions for generation and detection of recombination phonons with the energy of the superconducting gap 2W. Phonons are mediated between a niobium generator 1 and a Pb(In) detector 2 by a thin (Z 500 ˜) dielectric lead fluoride layer 3, showing a perfect phonon transmissivity at the generator/dielectric interface and a poor acoustical match at the detector/dielectric boundary. 1) The device has isolation, i.e., negligible effect of the output power on the input, which cannot be met by the QUITERON.

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Phonon-Mediated Quasiparticle Injection Transistor

Two superconducting tunnel junctions, separated by a thin dielectric layer for phonon transfer, form a three-terminal superconducting device which has good isolation characteristics. This article describes the use of superconducting tunnel junctions for generation and detection of recombination phonons with the energy of the superconducting gap 2W. Phonons are mediated between a niobium generator 1 and a Pb(In) detector 2 by a thin (Z 500 ~) dielectric lead fluoride layer 3, showing a perfect phonon transmissivity at the generator/dielectric interface and a poor acoustical match at the detector/dielectric boundary. 1) The device has isolation, i.e., negligible effect of the output power on the input, which cannot be met by the QUITERON. 2) Response is faster than the longest time constant observed in QUITERON operation, and will not occur in two extremely different time constants as encountered in QUITERON dynamics. This can be achieved by using a) a thin detector counterelectrode governed by quasi- particle diffusion, b) generator and detector materials with appropriate energy gaps, c) a detector bottom-film thickness which minimizes an enhancement of the quasiparticle recombination time by phonon trapping, but enables complete absorption of generator recombination phonons. 3) Improvement of current (power) gain is by a) quasiparticle overinjection generation in the detector bottom film (assigned to phonon absorption) via pair-breaking by generator recombination phonons. This process is twice as effective (same generator current, same injection volume, no phonon losses) as the usual direct tunneling injection (QUITERON operation); b) using a detector bottom-film superconductor with a much lower density of states at the Fermi level than niobium (used in QUITERON), such as lead; c) making the effective detector tunneling area as large as the generator tunneling area (not met in QUITERON design). Present QUITERON devices show a lack of isolation between the output and the input, i.e., the power dissipated in the quasiparticle detector affects the quasiparticle injector characteristic I(V) in the same order of magnitude as the injector power does the detector characteristic. This insufficiency, leading to an untolerable limitation of the fanout value, is in principle inherent in all three-film sandwich geometries forming two stacked tunnel junctions sharing a middle electrode. One way of improvement is to use a multiple (n) junction detector as realized in the QUITERON (n = 2). This article describes a device configuration with the main difference to QUITERON that the quasiparticles are exclusively injected into the detector via pair- breaking by the absorption of generator recombination phonons. The device exhibits excellent isolation. It can be used in a gap- suppression mode (QUITERON) as well as in an excess quasiparticle tunneling-current mode (superconducting transistor, quasip...