Sunao Ishihara

Improved resonance characteristics of GaAs beam resonators by epitaxially induced strain

Micromechanical-beam resonators were fabricated using a strained GaAs film grown on relaxed In0.1Ga0.9As∕In0.1Al0.9As buffer layers. The natural frequency of the fundamental mode was increased 2.5–4 times by applying tensile strain, showing good agreement with the model calculation assuming strain of 0.35% along the beam. In addition, the Q factor of 19 000 was obtained for the best sample, which is one order of magnitude higher than that for the unstrained resonator. This technique can be widely applied for improving the performance of resonator-based micro-/nanoelectromechanical devices.

High Quality Factor Graphene Resonator Fabrication Using Resist Shrinkage-Induced Strain

We used SU-8 shrinkage to fabricate strained graphene resonators to produce a high quality factor in a graphene resonator. A-few-layer graphene resonators were fabricated on a trench of an SU-8 resist. These resonators were clamped with diamond-like carbon (DLC), which was deposited by using focused-ion-beam chemical vapor deposition (FIB-CVD), and trimmed by using FIB etching. Annealing was used to apply tensile strain to the graphene resonators because SU-8 shrinks drastically. We also observed an increase in resonant frequency and quality factor in these graphene resonators after annealing. At room temperature, the quality factor of the best sample exceeded 7,000 for a resonator length of 10 µm.

High-sensitivity charge detection using antisymmetric vibration in coupled micromechanical oscillators

High-sensitivity charge detection using antisymmetric vibration in two coupled GaAs oscillators is demonstrated. The antisymmetric mode under in-phase simultaneous driving of the two oscillators disappears with perfect frequency tuning. The piezoelectric stress induced by a small gate-voltage modulation breaks the balance of the two oscillators, leading to the re-emergence of the antisymmetric mode. Measurement of the amplitude change enables detection of the applied voltage or, equivalently, added charges. In contrast to the frequency-shift detection using a single oscillator, our method allows a large readout up to the strongly driven nonlinear response regime, providing the high room-temperature sensitivity of 147 e/Hz0.5.

Force/displacement detection using quantum transport in InAs∕AlGaSb two-dimensional heterostructures

We fabricated a piezoresistive microelectromechanical cantilever that contains an InAs∕Al0.5Ga0.5Sb quantum well and measured the piezoresistance as a function of perpendicular magnetic field at 2.0K. The magneto-piezoresistance shows the feature of Schvnikov–de Haas oscillation, indicating a strong quantum effect on the piezoresistance. At the magnetic field that gives the largest piezoresistance, displacement and force sensitivities of 10−11m∕Hz and 10−12N∕Hz, respectively, were obtained.

In-situ Observation of the Three-Dimensional Nano-Structure Growth on Focused-Ion-Beam Chemical Vapor Deposition by Scanning Electron Microscope

To fabricate arbitrary three-dimensional (3-D) nanostructures, it is necessary to first understand the growth mechanism that occurs during focused-ion-beam chemical vapor deposition (FIB-CVD). With the aim of elucidating these details, we carried out in-situ observation of 3-D nanostructure growth during FIB-CVD using a scanning electron microscope (SEM) in a FIB/SEM dual-beam system. As a result, we demonstrated experimentally that the 3-D nanostructure growth depended on the beam profile of the FIB as well as the FIB irradiation time and scanning speed.

The fabrication of aligned pairs of gold nanorods in SiO2 films by ion irradiation

Pairs of gold nanodisks 40 or 70 nm in diameter were fabricated in silica by electron-beam lithography. On irradiation by 110 MeV Br(10+) ions, the nanodisks elongated to form nanorods; elongation occurred in the direction of propagation of the ions. The aspect ratios of the Au nanorods increased with increasing ion-flux density or fluence and with decreasing diameter of the nanodisks. The elongation mechanism can be explained in terms of a thermal spike model.

Growth of ultra-long free-space-nanowire by the real-time feedback control of the scanning speed on focused-ion-beam chemical vapor deposition

Free-space-nanowiring using focused-ion-beam chemical vapor deposition (FIB-CVD) has been demonstrated to enable the fabrication of various innovative three-dimensional (3D) nanodevices with overhanging structures. However, due to the change in growth characteristics, it is difficult to fabricate a free-space-nanostructure larger than several micrometers while keeping a uniform angle. Normally, the free-space-nanowire deviates downward from the starting angle after becoming approximately 2 μm long. In this study, the authors proposed a technology to fabricate ultralong horizontal free-space-nanowire by using the growth angle dependency of specimen current and carrying out feedback control of the scanning speed on Ga+ FIB. The feedback control system monitors the specimen current and controls the scanning speed of FIB in real-time while judging the value of specimen current. Ultralong horizontal free-space-nanowire with a length more than 30 μm and a length to thickness ratio as high as 300 was achieved. T...

Resistivity change of the diamondlike carbon, deposited by focused-ion-beam chemical vapor deposition, induced by the annealing treatment

Diamondlike carbon (DLC) deposited by focused-ion-beam chemical vapor deposition (FIB-CVD) has the interesting material characteristics because DLC deposited by FIB-CVD using the gallium (Ga) FIB contained Ga. The DLC wires were subjected to annealing, and it was found that their resistivity and the Ga content of DLC decreased. To understand the reason for the decrease in resistivity, changes in the fine structure and composition of DLC due to annealing were examined by transmission electron microscope electron energy loss spectroscopy and Rutherford backscattering spectroscopy/elastic recoil detection analysis, respectively. The results revealed that the graphite content of DLC increased due to hydrogen (H) elimination induced by annealing. Thus, it was concluded that the resistivity of the annealed DLC wires decreased due to the increase in the graphite content of DLC.Diamondlike carbon (DLC) deposited by focused-ion-beam chemical vapor deposition (FIB-CVD) has the interesting material characteristics because DLC deposited by FIB-CVD using the gallium (Ga) FIB contained Ga. The DLC wires were subjected to annealing, and it was found that their resistivity and the Ga content of DLC decreased. To understand the reason for the decrease in resistivity, changes in the fine structure and composition of DLC due to annealing were examined by transmission electron microscope electron energy loss spectroscopy and Rutherford backscattering spectroscopy/elastic recoil detection analysis, respectively. The results revealed that the graphite content of DLC increased due to hydrogen (H) elimination induced by annealing. Thus, it was concluded that the resistivity of the annealed DLC wires decreased due to the increase in the graphite content of DLC.

An overview of X-ray lithography

Current achievements and future prospects of SR base x-ray lithography are explained through an account of research and development efforts made by NTT LSI Laboratories. The SR lithography system, including the compact SR light source Super-ALIS and beamlines with efficient mirrors, is now at the stage of practical use. The vertical x-ray steppers SS-1 and SS-2 have attained a repeatability of overlay accuracy as high as 25 nm (3σ). High-accuracy x-ray masks can be fabricated by applying the multiple-exposure method. Further improvement in pattern placement accuracy is expected with application of distortion compensation writing. Intense efforts made in development of x-ray mask inspection and repair technology resulted in the fabrication of defect-free x-ray masks. Test fabrication of CMOS/SIMOX LSIs has yielded fully functional devices, with an improved overlay accuracy of 0.1 to 0.15 μm (3σ), and a CD control of ±10% in 0.2 μm regions. Further application of SR lithography to the test fabrication of future LSIs will prompt the implementation of this technology into the practical process.

Nanomechanical tuning forks fabricated using focused-ion-beam chemical vapor deposition

A theoretical and experimental investigation of nanomechanical tuning forks showed them to be mechanical resonators with high quality factors (Q-factors). For the theoretical calculation of resonant frequencies, the arm of a tuning fork was modeled by a beam connected to one or more torsional springs. Tuning forks with arm lengths of 3.6–6.9 μm were fabricated using focused-ion-beam chemical vapor deposition, and their resonant frequencies and Q-factors were measured with an optical instrument. The resonant frequencies calculated for vibrations in the two fundamental modes of the tuning forks (in-phase and antiphase) agreed well with the measured ones. When measured under mild vacuum (10 Pa), Q-factors for the tuning forks vibrating in the antiphase mode were as much as twice as high as those for nanomechanical cantilevers and tuning forks vibrating in the in-phase mode. In contrast, under atmospheric pressure, the Q-factors for the tuning forks vibrating in the in-phase mode were higher than those for th...