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Tunable coupled nanomechanical resonators for single-electron transport

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Published 4 November 2002 • Published under licence by IOP Publishing Ltd
, , Citation Dominik V Scheible et al 2002 New J. Phys. 4 86 DOI 10.1088/1367-2630/4/1/386

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1 Center for NanoScience and Fakultät für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany

2 Current address: Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974, USA.

Dates

  1. Received 23 August 2002
  2. Published

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1367-2630/4/1/86

Abstract

Nano-electromechanical systems (NEMS) are ideal for sensor applications and ultra-sensitive force detection, since their mechanical degree of freedom at the nanometre scale can be combined with semiconductor nano-electronics. We present a system of coupled nanomechanical beam resonators in silicon which is mechanically fully Q-tunable ~700-6000. This kind of resonator can also be employed as a mechanical charge shuttle via an insulated metallic island at the tip of an oscillating cantilever. Application of our NEMS as an electromechanical single-electron transistor (emSET) is introduced and experimental results are discussed. Three animation clips demonstrate the manufacturing process of the NEMS, the Q-tuning experiment and the concept of the emSET.

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Figure 2 (746 KB, 3 MB AVIs) Animation clip DivX encoded: nems.DivX.avi; Cinepak encoded: nems.CPK.avi. Manufacturing process. (a) The SOI-chip is coated with PMMA (b) as a resist for electron-beam lithography and the NEMS layout is transferred by electron-beam writing (c). After resolving the exposed acrylate (d) the bare silicon is coated (e) first with a layer of NiCr, a Au metal layer and an Al protection layer (shown as only one). Subsequent lift-off of the metal film (f) prepares the sample for dry etching (g), which defines the nanostructure. The SiO2 is removed selectively in a buffered oxide etchant (h) and dried using critical point drying (not shown).

Figure 2 (746 KB, 3 MB AVIs) Animation clip DivX encoded: nems.DivX.avi; Cinepak encoded: nems.CPK.avi. Manufacturing process. (a) The SOI-chip is coated with PMMA (b) as a resist for electron-beam lithography and the NEMS layout is transferred by electron-beam writing (c). After resolving the exposed acrylate (d) the bare silicon is coated (e) first with a layer of NiCr, a Au metal layer and an Al protection layer (shown as only one). Subsequent lift-off of the metal film (f) prepares the sample for dry etching (g), which defines the nanostructure. The SiO2 is removed selectively in a buffered oxide etchant (h) and dried using critical point drying (not shown).

Figure 3 (750 KB, 3 MB AVIs) Animation clip DivX encoded: Qtuning.DivX.avi; Cinepak encoded: Qtuning.CPK.avi. The Q-tuning experiment. (a) Resonance frequencies do not match for the base mode M1 and only the central beam is excited mechanically. (b) The centre of mass is not fixed in space and hence the structure possesses a poor Q. (c) Additional driving of the outer cantilevers with a resonance-matched frequency close to f1 renders the system's centre of mass fixed in space, and consequently enhances the Q-factor (d). Insets show experimental data (mechanical response Pref versus frequency f) for each situation.

Figure 3 (750 KB, 3 MB AVIs) Animation clip DivX encoded: Qtuning.DivX.avi; Cinepak encoded: Qtuning.CPK.avi. The Q-tuning experiment. (a) Resonance frequencies do not match for the base mode M1 and only the central beam is excited mechanically. (b) The centre of mass is not fixed in space and hence the structure possesses a poor Q. (c) Additional driving of the outer cantilevers with a resonance-matched frequency close to f1 renders the system's centre of mass fixed in space, and consequently enhances the Q-factor (d). Insets show experimental data (mechanical response Pref versus frequency f) for each situation.

Figure 4 (640 KB, 3 MB AVIs) Animation clip DivX encoded: mset.DivX.avi; Cinepak encoded: mset.CPK.avi. concept of a mechanical single-electron transistor, illustrated for g · n = 1. (a) A tiny island of gold (size 100 nm × 100 nm × 100 nm) is shuttled back and forth between source and drain contact. Excitation is achieved via mechanical coupling. (b) Crucial for Coulomb blockade are the two capacitances CS and CD (the gate has been left out for clarity). Once the source contact is biased at a voltage V (c) a fractional voltage VI is applied to the island (d). Deflection of the cantilever toward the source gate (e) causes the left tunnel barrier to become surmountable, and an electron tunnels (f). When the bias, capacitances and temperature satisfy the Coulomb-blockade condition (3) further electron tunnelling is blocked (g), and the NEMS shuttle transports a single electron each cycle (h). The inset of the initial frame and (h) shows number of transferred electrons g · n versus excitation frequency f for a set of input (driving) powers Pin, as calculated via (4) from actual experimental data.

Figure 4 (640 KB, 3 MB AVIs) Animation clip DivX encoded: mset.DivX.avi; Cinepak encoded: mset.CPK.avi. concept of a mechanical single-electron transistor, illustrated for g · n = 1. (a) A tiny island of gold (size 100 nm × 100 nm × 100 nm) is shuttled back and forth between source and drain contact. Excitation is achieved via mechanical coupling. (b) Crucial for Coulomb blockade are the two capacitances CS and CD (the gate has been left out for clarity). Once the source contact is biased at a voltage V (c) a fractional voltage VI is applied to the island (d). Deflection of the cantilever toward the source gate (e) causes the left tunnel barrier to become surmountable, and an electron tunnels (f). When the bias, capacitances and temperature satisfy the Coulomb-blockade condition (3) further electron tunnelling is blocked (g), and the NEMS shuttle transports a single electron each cycle (h). The inset of the initial frame and (h) shows number of transferred electrons g · n versus excitation frequency f for a set of input (driving) powers Pin, as calculated via (4) from actual experimental data.

10.1088/1367-2630/4/1/386