Masayoshi Esashi

Precise motion control of a nanopositioning PZT microstage using integrated capacitive displacement sensors

We propose a hysteresis and drift compensation scheme using proportional-integral feedback control for a nanopositioning Pb(ZrTi)O3 (PZT) microstage. A multi-degree of freedom PZT microstage with integrated differential capacitive displacement sensors has been fabricated and tested, demonstrating the feasibility of compensating for hysteresis and creep. The feedback signal to the PZT actuators is fed from differential capacitive sensors of the displacement of the microstage. Experimental results show that the sensitivity of the displacement sensor is approximately 0.53 V µm−1. A maximum resolution of 16 nm is achieved when hysteresis is compensated for, and the minimum detectable variation of capacitance ΔC is 1.25 × 10−3 pF. The hysteresis of the system varies with the proportional gain Kp, integral time constant Ti and reference input frequency. By using feedback control with a proportional and integration (PI) controller, the hysteresis decreases from 30% in open-loop operation to approximately 1% in closed-loop operation at a gain of 20, when the frequency of the sine reference input is 1 Hz and Ti is 20 ms. Efficient compensation of hysteresis is validated by the closed-loop control, especially when the frequency of the reference input is low. Elimination of creep/drift is also verified by the closed-loop control.

Mass sensing with resonating ultra-thin silicon beams detected by a double-beam laser Doppler vibrometer

This paper reports on mass sensing with 33 nm thick single-crystalline cantilevers by a double-beam laser Doppler vibrometer. The resonant frequency of an oscillating thin cantilever beam is very sensitive to a loaded mass. However, the drift of the resonance, due to gas adsorption and mechanical instability, limits the minimum detectable mass in general. Two cantilevers for sensing and its reference will compensate their influences. Two cantilevers were made to self-oscillate by electrostatic actuation at different resonant frequencies. A 10 pg sample (a particle of organosilicon monomer) was mounted at the end of one cantilever, and thermogravimetry of the sample using the two cantilevers was demonstrated. The cantilevers were heated up by a heater in vacuum, and the change in mass was detected from the change in resonant frequency. The exact temperature change can be estimated from the change in resonant frequency of one cantilever as a reference. The derivative of the frequency change, corresponding to desorbed mass, clearly shows a peak of mass desorption at about 270 °C.

Parametrically amplified thermal resonant sensor with pseudo-cooling effect

In this paper, a resonating thermal sensor with the capability of de-amplifying thermal noises based on mechanical parametric amplification is presented. A single-crystalline silicon resonator is formed at the edge of an absorber that is freely suspended by narrow beams, and the resonant frequency of the resonator is changed by both heat conduction and thermal stress in irradiating IR radiation. An electrode for electrostatically vibrating near the resonant frequency is integrated, and two electrodes for electrostatically exciting parametric amplification are also formed near the resonator. We propose a scheme in which the frequency fluctuation of the mechanical vibration can be reduced by noise-squeezing involved in parametric amplification under an appropriate condition, resulting in improvement of the noise equivalent power and normalized detectivity. In this research, the prototype of thermal resonant IR sensors was fabricated in order to verify the scheme of the noise-squeezing, and currently parametric resonance with the noise-squeezing in the resonator is confirmed and the fundamental characteristics of the prototype are reported.

Capacitive resonant mass sensor with frequency demodulation detection based on resonant circuit

In this letter, capacitive mass sensing with a 250-nm-thick single-crystalline silicon cantilever is investigated. The mass sensor employs the frequency modulation detection method using an electrical LC oscillator, in which the capacitance of the sensor serves as the component of the oscillator. The displacement noise of the demonstrated capacitive detection is 0.05nm∕(Hz)0.5, which is equivalent to the capacitance change of 2.4×10−21F. It is experimentally shown that the capacitive detection is less affected to temperature fluctuation noise than optical detection. The detectable minimum mass of 1×10−14g is achieved using capacitive detection in ambient atmosphere.

Modeling and experimental validation of the performance of a silicon XY-microstage driven by PZT actuators

In this paper, the design and evaluation of silicon-based PbZrTiO3 (PZT) driven XY-microstages with total dimensions of 20 × 20 × 0.4 mm3 are presented. The PZT actuator has the advantage of having high accuracy and high intrinsic resonance frequency. However, its displacement is very small; thus Moonie amplification mechanisms are integrated to magnify the displacement. Finite element method simulation is carried out to obtain the microstage performance and identify its design parameters. It is demonstrated that an amplification factor of up to 18 times is possible using the silicon Moonie amplification mechanism, resulting in displacements of 82 µm and 60 µm at an applied voltage of 70 V for the X and Y directions, respectively. Furthermore, this microstage produces resonance frequencies of 261 Hz and 642 Hz in the X and Y directions, respectively.

Resonator combined with a piezoelectric actuator for chemical analysis by force microscopy

A high frequency silicon resonator for dynamic scanning force microscopy is combined with an integrated piezoelectric actuation element for large displacements. A high resonance frequency is required for imaging on the nanometer scale, and a large displacement is needed for the chemical analysis of the material at the end of the probe. The small piezoelectric resonator is formed at the end of a long piezoelectric actuator using a silicon micromachining technology. The resonator can be oscillated at 96.4 kHz, and the actuator generates a maximum displacement of 15 microm at the end of the probe. The dynamic-mode scanning force microscopy capability, using the integrated piezoelectric resonator, is demonstrated on a 2 microm pitch Au grating.

Development of high-resolution intraluminal and intravascular MRI probe using microfabrication on cylindrical substrates

The objective of this study is development of high-resolution intraluminal and intravascular MRI probe using microfabrication on cylindrical substrates. MRI holds promise for in vivo characterization due to its potential for obtaining high-resolution images and its sensitivity to the compositional characteristics of lesion. By placing a receive coil in the human body, NMR signals from the tissue surrounding the coil can be detected sensitively and the method enables in vivo high-resolution imaging (high spatial resolution and high spectroscopic resolution). The preferable receive coil has homogeneous RF receptivity around the probe and high-SNR. Novel coil designs and/or multi-coil have capabilities to meet these demands. To connect the tuning/matching circuit and amplifier circuit near the coil is needed to improve SNR of the system. Microfabrication on cylindrical substrate is one of methods for fabricating arbitrary coil pattern and the tuning/matching circuit on the tube with small diameters. Using a maskless lithography technique, solenoid coil, tilted coil and saddle shaped coil have been fabricated on glass tube with 2 mm O.D.. Imaging test of the coils were performed on 3 T MRI in a 2% agar phantom.

Fabrication of piezoresistive nanocantilevers for ultra-sensitive force detection

This paper presents the design, fabrication and characterization method of piezoresistive nanocantilevers for ultra-sensitive force detection application. A shallow boron-doped layer as thin as 40 nm is achieved using spin-on diffusion. The piezoresistive nanocantilevers are patterned by electron beam (EB) lithography and fast atom beam (FAB) etching. The resonance response of the nanocantilevers is characterized by both optical readout using a laser Doppler vibrometer and piezoresistive self-detection. A soft spring effect is detected in the nanocantilevers.

Photolithographic fabrication of gated self-aligned parallel electron beam emitters with a single-stranded carbon nanotube

In this paper we report on the development of a photolithographic process to fabricate a gated-emitter array with single-stranded carbon nanotubes (CNTs) self-aligned to the center of the emitter gate using plasma-enhanced chemical vapor deposition (PECVD). Si tips are formed on a silicon wafer by anisotropic etching of Si using SiO(2) as a mask. Deposition of a SiO(2) insulating layer and Cr-W electrode layers creates protrusions above the Si tips. This wafer is polished, and the Cr-W on the tips is removed. Etching of the SiO(2) using hydrofluoric acid is performed to expose the gated Si tip. Incorporation of a novel diffusion process produces single-stranded CNTs by depositing a thin Ni layer on the Si tips and thermally diffusing the Ni layer to yield a catalyst particle for single-stranded CNT growth. The large surface to volume ratio at the apex of the Si tip allows a Ni particle to remain to act as a catalyst to grow a single-stranded CNT for fabricating the CNT based emitter structure. Diffusion of the Ni is carried out in situ during the heating phase of the PECVD CNT growth process at 600u2009°C. The diameters of the observed CNTs are on the order of 20xa0nm. The field emission characteristics of the gated field emitters are evaluated. The measured turn-on voltage of the gated emitter is 5xa0V.

Conductive polymer patterned media fabricated by diblock copolymer lithography for scanning multiprobe data storage

A conductive polymer dot pattern has been fabricated as a patterned medium using diblock copolymer lithography (DCL) for scanning multiprobe data storage systems (SMDSSs). DCL can easily provide a higher dots pattern density than that obtained using electron beam lithography. For DCL, the microphase-separated structure of polystyrene-block-polymethylmethacrylate is utilized. Then, the closed dot pattern of polyaniline (PANI) with a center to center distance of adjacent dots of 30xa0nm is fabricated by DCL. Electrical modification experiments of the fabricated PANI dots are demonstrated using scanning probe microscopy (SPM). As a result, the conductivities of the modified dots are selectively changed by applying modification voltages with the tip of the SPM probe. Recording on the conductive polymer with 30xa0nm pitch at the minimum can be demonstrated, which corresponds to a recording density of ∼700xa0Gbitsxa0inch(-2). These results show that the conductive polymer patterned medium has the potential ability to achieve high-density recording for SMDSSs.