Single-charge tunneling device

Abstract

A single-electron transistor ( 1 ) has an elongate conductive channel ( 2 ) and a side gate ( 3 ) formed in a 5 nm-thick layer ( 4 ) of Ga 0.98 Mn 0.02 As. The single-electron transistor ( 1 ) is operable, in a first mode, as a transistor and, in a second mode, as non-volatile memory.

1 . A magnetoresistance single-charge tunnelling device comprising:
 first and second leads;   a conductive island having a charging energy of at least 1 meV and arranged such that charge is transferable from the first lead to the second lead via the conductive island; and   a gate for changing an electrostatic energy of the conductive island;   wherein at least one, but not all, of said first lead, second lead, island and the gate comprises a ferromagnetic material which includes a rare earth element and/or a transition metal;   wherein (i) the first and second leads are ferromagnetic but are configured such that one is not pinned relative to the another, (ii) the first or second lead is not ferromagnetic, or (iii) the first and second leads are not ferromagnetic; and   wherein the single-charge tunnelling device exhibits an anisotropic magnetoresistance effect.   
     
     
         2 . A device according to  claim 1  wherein the island is ferromagnetic. 
     
     
         3 . A device according to  claim 1 , wherein the gate is ferromagnetic. 
     
     
         4 . A device according to  claim 1 , wherein said rare earth metal is Dy, Er or Ho. 
     
     
         5 . A device according to  claim 1 , wherein said transition metal is a noble metal. 
     
     
         6 . A device according to  claim 5 , wherein the noble metal is Pt or Pd. 
     
     
         7 . A device according to  claim 1 , wherein the ferromagnetic material comprises Fe or Co. 
     
     
         8 . A device according to  claim 1 , comprising at least two islands arranged such that charge is transferable from the first lead to the second lead via at least one of the at least two conductive islands. 
     
     
         9 . A device according  claim 1 , wherein a one of the first lead, second lead, island or gate which is ferromagnetic exhibits a change in chemical potential which is at least 6 meV or at least 9 meV in response to rotation of magnetization from a first orientation to a second orientation which is not parallel or anti-parallel to the first orientation. 
     
     
         10 . A non-volatile memory comprising a device according to  claim 1 . 
     
     
         11 . A magnetic field sensor comprising a device according to  claim 1 . 
     
     
         12 . Apparatus, comprising:
 a device according to  claim 1 ; and   a magnetic field source which is configured to apply a magnetic field to the single-charge tunnelling device such that magnetization is rotated from a first orientation to a second orientation which is not parallel or anti-parallel to the first orientation.   
     
     
         13 . A magnetoresistance single-charge tunnelling device comprising:
 first and second leads; and   a conductive island having a charging energy of at least  1  meV and arranged such that charge is transferable from the first lead to the second lead via the conductive island;   wherein at least one, but not all, of the first lead, second lead and island comprises a ferromagnetic material which includes a rare earth element and/or a transition metal,   wherein i) the first and second leads are ferromagnetic but are configured such that one is not pinned relative to the another, (ii) the first or second lead is not ferromagnetic, or (iii) the first and second leads are not ferromagnetic; and   wherein the single-charge tunnelling device exhibits an anisotropic magnetoresistance effect.   
     
     
         14 . A non-volatile memory comprising a device according to  claim 13 . 
     
     
         15 . A magnetic field sensor comprising a device according to  claim 13 . 
     
     
         16 . Apparatus, comprising:
 a device according to  claim 13 ; and   a magnetic field source which is configured to apply a magnetic field to the single-charge tunnelling device such that magnetization is rotated from a first orientation to a second orientation which is not parallel or anti-parallel to the first orientation.   
     
     
         17 . A method of operating a single-charge tunnelling device comprising first and second leads, a conductive island having a charging energy of at least 1 meV and arranged such that charge is transferable from the first lead to the second lead via the conductive island and a gate for changing an electrostatic energy of the conductive island, at least one, but not all, of said first lead, second lead, island and the gate comprises a ferromagnetic material includes a rare earth element and/or a transition metal, wherein (i) the first and second leads are ferromagnetic but are configured such that one is not pinned relative to the another, (ii) the first or second lead is not ferromagnetic, or (iii) the first and second leads are not ferromagnetic, and wherein the single-charge tunnelling device exhibits an anisotropic magnetoresistance effect, the method comprising:
 applying a first bias to the gate;   removing said first bias from the gate;   measuring a first resistance between the leads;   applying a second, different bias to the gate;   removing said second bias from the gate; and   measuring a second resistance between the leads such that the first and second resistances differ.   
     
     
         18 . A method according to  claim 17 , wherein applying the first bias causes magnetization to be rotated from the first orientation to the second orientation and applying the second bias causes magnetization to be rotated from the second orientation to a third orientation which is not parallel or anti-parallel to the first orientation. 
     
     
         19 . A method of operating a single-charge tunnelling device comprising first and second leads, a conductive island having a charging energy of at least 1 meV and arranged such that charge is transferable from the first lead to the second lead via the conductive island, at least one, but not all, of said first lead, second lead and island comprises a ferromagnetic material includes a rare earth element and/or a transition metal, wherein (i) the first and second leads are ferromagnetic but are configured such that one is not pinned relative to the another, (ii) the first or second lead is not ferromagnetic, or (iii) the first and second leads are not ferromagnetic and wherein the single-charge tunnelling device exhibits an anisotropic magnetoresistance effect, the method comprising:
 applying a first magnetic field;   removing the first magnetic field;   measuring a first resistance between the leads;   applying a second, different magnetic field;   removing the second magnetic field; and   measuring a second resistance between the leads such that the first and second resistances differ.   
     
     
         20 . A method according to  claim 19 , wherein applying the first magnetic field causes magnetization to be rotated from the first orientation to the second orientation and applying the second magnetic field causes magnetization to be rotated from the second orientation to a third orientation which is not parallel or anti-parallel to the first orientation.