Norimasa Yoshimizu

Scanning probe nanoscale patterning of highly ordered pyrolytic graphite.

In this work we present precision scanning probe etching of highly ordered pyrolytic graphite. We corroborate that the lithography is due to an electrochemical, polarity-dependent, meniscus-mediated etching of the carbon surface. By changing the etching temperature, we are able to reduce the feature size by 24%. External feedback control and probe tip cleaning enables desired cut patterns with high precision. Using a feedback-controlled atomic force microscope, we demonstrate an array of 105 trenches using 370 etching operations, with 136 +/- 6 and 183 +/- 5 nm precision over an area of 2.5 microm x 2.5 microm. This results in a precision of 4.4% and 2.7%, respectively.

Self-powered near field electron lithography

Electron beam exposure is the tool of choice for highest resolution lithography but suffers from the low throughput during serial beam writing [T. Ito and S. Okazaki, Nature (London) 406, 1027 (2000); R. F. Pease and S. Y. Chou, Proc. IEEE 96, 248 (2008)]. The authors designed and developed a low-cost self-powered near-field electron lithography (SPEL) technique, which utilizes the spontaneously emitted energetic electrons from beta-emitting radioisotope thin films. This approach enables massively parallel e-beam lithography, with potentially arbitrarily large concurrently exposed surface area, controlled by the size of the radioactive source. This method potentially eliminates the need for vacuum systems and the electron focusing column as needed in the existing electron beam lithography systems. This will greatly simplify the overall lithographic system and reduce the cost of deep-subnanometer lithography. In SPEL system, emitted electrons are spatially blocked using a nanostenciled micromachined mask t...

Nanometrology optical ruler imaging system using diffraction from a quasiperiodic structure

This work demonstrates wafer-scale, path-independent, atomically-based long term-stable, position nanometrology. This nanometrology optical ruler imaging system uses the diffraction pattern of an atomically stabilized laser from a microfabricated quasiperiodic aperture array as a two-dimensional optical ruler. Nanometrology is accomplished by cross correlations of image samples of this optical ruler. The quasiperiodic structure generates spatially dense, sharp optical features. This work demonstrates new results showing positioning errors down to 17.2 nm over wafer scales and long term stability below 20 nm over six hours. This work also numerically demonstrates robustness of the optical ruler to variations in the microfabricated aperture array and discretization noise in imagers.

Nano-electromechanical zero-dimensional freestanding nanogap actuator

Micromachined free standing nanogap with metal electrodes is presented. The gap size is as small as 17 nm, and can be reduced further with electrostatic or piezoelectric actuation. The nanoscale gap is fabricated by industrial standard optical lithography and anisotropic wet chemical Si etching. Electron transport between the metal electrodes with optical stimulus enhancing photon-electron coupling (plasmon) is presented.

Nanometrology Using a Quasiperiodic Pattern Diffraction Optical Ruler

This paper presents a nanometrology optical ruler imaging system to enable rapid wafer-scale nanometrology, particularly for scanning probe microscopes. The ruler is generated by the diffraction of a 10-8 stabilized laser by a metal thin-film pattern. Microfabrication techniques create a high-count quasiperiodic aperture array in the film which generates a translationally asymmetric feature-dense optical diffraction pattern well suited for the nanometrology application. An imager array samples the optical ruler and calculates its position by Fourier transform cross-correlation methods. Numerically, it is found that improving the imager by pixel count and size can reduce positioning errors down to 1/120th of the pixel size, after which further improvements yield no reduction in error. Experiments using a modest complementary metal-oxide-semiconductor imager demonstrate a positioning accuracy of 1/124th of the pixel size, or 29 nm. This system will enable high-precision high-throughput metrology and fabrication of nano- and microelectromechanical systems.

Electroluminescence from a suspended tip-synthesized nano ZnO dot

Electroluminescence (EL) from a laterally suspended nano ZnO dot (LSNZD) integrated between two microfabricated atomically sharp probe-tips is presented. When driven by 1 μA of bias current, the LSNZD emitted light, which was easily observed by the naked eye at room temperature. The minimum number of photons emitted per a second from the LSNZD was ∼9000/s at 100 nA of current, when driven by 12.5 V. The light emission mechanism and electrical characteristics of the LSNZD are explained with a metal-semiconductor-metal model. An optical wavelength spectrum of the emitted light shows major bands of emitted photons between 580 and 750 nm, which indicates the electron transitions from defects in the ZnO band gap. The device fabrication is compatible with typical integrated circuit processes and is suitable for chip- scale optoelectronics.

Tip-based patterning of HOPG and CVD graphene

Nanometer-scale patterning of graphite and graphene has been accomplished through local anodic oxidation using an AFM tip. The underlying mechanism is explained. To date, protrusions, holes, trenches, and even words have been patterned in HOPG over scales ranging from 1nm2 to 1mm2 and depths ranging from sub nm to as deep as 200nm with less than 5 nm variation on the feature size and placement. This same method has also been applied to CVD-grown graphene providing a resist-free process for patterning graphene at the single nanometer scale. This capability could provide a method to rival e-beam lithography resolution but without any pre- or post-processing.

Near-kT switching-energy lateral NEMS switch

We present a novel architecture of pre-biased N/MEMS switch that has an effective turn-on voltage as low as 300µV (~ (kT/q)/87), operating in a regime without electrostatic pull-in. The very sharp sub-threshold slope of current transduction enables deep sub<kT/q voltages to be used for switch operation. The switching energy can be exceptionally low, only ~2kT, coming close to the quantum-mechanical switch energy as predicted at kT. Nanomechanical switches in series with transistor technologies (BJTs, CMOS, or MESFETs) can facilitate ultra low-power circuits by eliminating leakage current in transistor circuits. Furthermore, the new switch architecture could facilitate all-mechanical digital logic that might consume even less power than hybrid solutions, and the switches are naturally radiation hard.

MEMS Diffractive Optical Nanoruler Technology for Tipbased Nanofabrication and Metrology

This paper reports on a diffractive optical nanoruler used to guide tip-based nanofabrication. A precision of ±3 × 10-4 has been demonstrated across a 75 mm wafer; we can account for errors external to the system which reduce this figure to ±1.5 × 10-5. A microfabricated aluminum grating diffracts an external cavity laser beam stabilized to the rubidium D2 line (780nm). The resulting hexagonal lattice intensity pattern guides a PC-board assembly, consisting of a quadrature photodiode and an STM tip, on a flexural piezo stage. The STM tip is used to make indentations in resist spun on an Al film deposited on a silicon wafer. The precision is measured using electron microscopy by locating the indentations.

Electroluminescence from a freestanding integratable single ZNO dot

We present electroluminescence (EL) from a free standing isolated single ZnO dot device integrated on a microfabricated probe-tip interface. EL from the device in ambient conditions at room temperature has been observed by the naked eye at a bias current of 1 µA. The device fabrication is compatible with CMOS processing and is suitable for chip-scale optoelectronics. This device is shown to be capable of emitting one photon at a time, which is useful for many NEMS and MEMS sensors.