Single Electron Devices Vishwanath Joshi Advanced Semiconductor Devices

Single Electron Devices Vishwanath Joshi Advanced Semiconductor Devices EE 698 A

Outline n n n Introduction Single Electron (SE) Transistor SE Turnstiles SE Pump SE Inverters q n Metal, Semiconductor, Carbon nano-tube SE Memory

Introduction n Devices that can control the motion of even a single electron Consist of quantum dots with tunnel junctions Simplest device q Single electron box

Single electron box n Conditions for observing single electron tunneling phenomena q Ec > kb. T n q Ec = e 2/2 CΣ Rt > Rk n Rk = h/e 2 (25. 8 KOhms)

Single electron transistor n 3 terminal switching device Current flows when Vg = ne/2 Cg

Turnstile n n n Single electron is transferred per cycle of an external RF signal ΔEk = -e(|Q|k – Qck)/Ck Qck = e(1+Cek/Ck)/2 Cek = capacitance of circuit in parallel with junction k Ck = junction capacitance Frequency Locked Turnstile Device for Single Electrons, Physical Review Letters, Vol 64(22), 28 May 1990, 2691

Pumps Accuracy of electron counting using a 7 -junction electron pump, Applied Physics Letters, Vol 69 (12), 16 Sept 1996, 1804

Pumps (contd. ) n n n Al/Al 2 O 3 structures have limited operational temperature and poor operational stability Si-based SETs operate at higher temperature Place MOSFETs near SET – control of channels Electron pump by combined single-electron/field effect transistor structure, Applied Physics Letters, Vol 82 (8), 24 Feb 2003, 1221

Fabrication n n Fabricated on SOI substrate using standard MOS process Formation of Si island by PADOX method Dual gates made of Phosphorous doped poly -Si are defined Again deposit Phosphorous doped poly-Si and define a broad gate covering entire pattern

Measurements n n n Measurements at 25 K Vth of MOSFET 1 = 0. 3 V Vth of MOSFET 2 =-0. 2 V

Charge Coupled Device n 30 nm wide Si-wire channel and poly-Si gates defined by E-beam lithography Current quantization due to single electron transfer in Si-wire charge coupled device, Applied Physics Letters, Vol 84 (8), 23 Feb 2004, 1323

Si SE Inverter n Twin Si single electron islands are formed by V-PADOX Si complementary single-electron inverter with voltage gain, Applied Physics Letters, Vol 76 (21), 22 May 2000, 3121

SE Inverter (contd. ) n Working of Inverter

Si SE Inverter (contd. )

Al/Al 2 O 3 SE Inverter n n n 25 nm thick Al patterned to form the lower electrodes Al oxidized in an O 2 plasma, 200 m. Torr, 5 min, 200 o. C Second Al deposition Single-electron inverter, Applied Physics Letters, Vol 78 (5), 19 Feb 2001, 1140

Al/Al 2 O 3 SE Inverter (contd. ) n Working of Inverter

SE Inverter from carbon nanotubes n Tunnel barriers fabricated with the local irradiation of an Ar beam Fabrication of single-electron inverter in multiwall carbon nanotubes, Applied Physics Letters, Vol 82 (19), 12 May 2003, 3307

SE Inverter from carbon nanotubes (contd. ) n Working of the Inverter

Memory

References n n n n Frequency Locked Turnstile Device for Single Electrons, Physical Review Letters, Vol 64(22), 28 May 1990, 2691 Accuracy of electron counting using a 7 -junction electron pump, Applied Physics Letters, Vol 69 (12), 16 Sept 1996, 1804 Electron pump by combined single-electron/field effect transistor structure, Applied Physics Letters, Vol 82 (8), 24 Feb 2003, 1221 Current quantization due to single electron transfer in Si-wire charge coupled device, Applied Physics Letters, Vol 84 (8), 23 Feb 2004, 1323 Si complementary single-electron inverter with voltage gain, Applied Physics Letters, Vol 76 (21), 22 May 2000, 3121 Single-electron inverter, Applied Physics Letters, Vol 78 (5), 19 Feb 2001, 1140 Fabrication of single-electron inverter in multiwall carbon nanotubes, Applied Physics Letters, Vol 82 (19), 12 May 2003, 3307 A high-speed silicon single-electron random access memory, IEEE Electron Device Letters, Vol. 20, No. 11, November 1999, 583