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Josephson Transistor

IP.com Disclosure Number: IPCOM000051475D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 65K

Publishing Venue

IBM

Related People

Rajeevakumar, TV: AUTHOR

Abstract

This article relates to a superconducting transistor which utilizes the dynamic properties of Josephson vortices. The superconducting transistor is essentially a Josephson tunnel junction 1 with large width to Josephson penetration depth ratio [1], W/Lambda(J), and small length to Josephson penetration depth ratio, L/Lambda(J), as shown in Fig. 1a and Fig. 1b. A control line 2 of width W(c), which can carry two independent control currents I(C1) and I(C2), passes over junction 1.

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Josephson Transistor

This article relates to a superconducting transistor which utilizes the dynamic properties of Josephson vortices. The superconducting transistor is essentially a Josephson tunnel junction 1 with large width to Josephson penetration depth ratio [1], W/Lambda(J), and small length to Josephson penetration depth ratio, L/Lambda(J), as shown in Fig. 1a and Fig. 1b. A control line 2 of width W(c), which can carry two independent control currents I(C1) and I(C2), passes over junction 1.

Inverting as well as non-inverting operation of the transistor is performed as follows: Junction is first biased with a gate current I(g). (Here I(g) < I(o) where I(C1) is the maximum zero-voltage current at I(C1,2)=O.) When a control current I is applied such that B(I(C1)) = <i(o)O(C1) Mu(o) I (C1) over W(c) <B(C1) of the junction 1, junction 1 makes a transition to a mixed state. In the presence of I(C1), unipolar currant vortices are continuously formed inside the junction and are pushed out by bias current Ig. As a result, the junction switches from zero- voltage to a vortex flow/o/ branch [2]. (See Figs. 2a and 2b.) These are the operating conditions of the proposed transistor.

Now, the voltage position of the vortex-flow branch can be varied by a second control current I(C2) through See Original. where c is the speed of electromagnetic waves in junction 1, Lambda(1) and Lambda(2) are the London penetration depths of the two-junction electrodes, Mu(o) is the permeability of free space, and 1 is the thickness of the oxide barrier [3]. The removal of I(C2) brings the vortex-flow branch back to the original voltage position. Hence, the device is non-latching. Depending on the voltage position of the vortex-flow branch, a current will be transferred to a load connected across junction 1. Thus, the magnitude of the current through the load is directly proportional to I(C2). (See Fig. 2c.) For inverting operation, a larger I(C1) is initially applied and then I in the opposite direction to I(C1). Good current gain can be obta...