We have developed and operated a newly conceived multiprobe scanning force microscope (SFM) using microfabricated piezoelectric cantilevers. An array of piezoelectric microcantilevers with a piezoelectric ZnO layer on an SiO2 film makes it possible to build a multiprobe SFM system. Multiprobe SFMs are required for the application of SFM to the probe lithography and high density data storage. Each cantilever probe of multiprobe system should have a detector for sensing of its own deflection and an actuator for positioning of its tip. The piezoelectric cantilever can detect its own vibration amplitude by measuring the piezoelectric current, and it can also drive its tip by applying a voltage to the piezoelectric layer. Therefore, the piezoelectric cantilever is suitable for each cantilever of the array in the multiprobe SFM. We have verified the applicability of the piezoelectric cantilever to each lever of the array by characterizing the sensitivities of the deflection sensing and actuation. The ZnO piezoelectric cantilever with the length of 125 µm works as the z scanner with the sensitivity of 20 nm/V. We have also fabricated an experimental piezoelectric microcantilever array with ten cantilevers. We have constructed parallel operation SFM system with two cantilevers of the fabricated array and successfully obtained parallel images of 1 µm pitch grating in constant height mode.

We study ultrafast operation of multiple-valued quantizers composed of resonant-tunneling diodes (RTDs) and high electron mobility transistors (HEMTs). The operation principle of these quantizers is based on the monostable-multistable transition logic (MML) of series-connected RTDs. The quantizers are fabricated by monolithically integrating InP-based RTDs and 0.7-µm-gate-length HEMTs with a cutoff frequency of 40 GHz. To perform high-frequency experiments, an output buffer and termination resistors are attached to the quantizers, and the quantizers are designed to accommodate high-frequency input signals. Our experiments show that both ternary and quaternary quantizers can operate at clock frequencies of 10 GHz and at input frequencies of 3 GHz. This demonstrates the potential of applying RTD-based multiple-valued quantizers to high-frequency circuits.

A novel delta-sigma modulator that utilizes a resonant-tunneling diode (RTD) quantizer is proposed and its operation is investigated by HSPICE simulations. In order to eliminate the signal-to-noise-and-distortion ratio (SINAD) degradation caused from the poor isolation of a single-stage quantizer (1SQ), a three-stage quantizer (3SQ), which consists of three cascoded RTD quantizers, is introduced. At a sample rate of 10 Gsps (samples per a second) and a signal bandwidth of 40 MHz (oversampling ratio of 128), the modulator demonstrates a SINAD of 56 dB, which corresponds to the effective number of bits of 9.3.

Along with the sophistication of society, the requirements for infrastructure systems are also becoming more sophisticated. Conventionally, infrastructure systems have been accepted if they were safe and stable, but nowadays they are required for serviceability as a matter of course. For this reason, not only the expansion of the scope of the control system but also the integration with the information service system has been frequently carried out. In this paper, we describe safety technology based on autonomous decentralized technology as one of the measures to secure safety in a control system integrating such information service functions. And we propose its future studies.

This paper reports on a new dynamic scanning force microscope (SFM), in which the piezoelectric microcantilever is utilized for the lever excitation and displacement sensing. Piezoelectric cantilevers can detect their deflection without external sensing elements and be vibrated with no oscillator outside. The cantilever integrated with the deflection detector and the oscillator changes the conventional construction of a dynamic SFM and expands its range of applicability. The microcantilever used consists of a ZnO layer sandwiched with Au electrodes deposited on a thin beam of thermally grown SiO2. The length, width and thickness of the lever are 125 µm, 50 µm and 3.5 µm, respectively. We have characterized this cantilever by measuring the charge spectrum and the frequency dependence of the admittance. From the charge spectrum the mechanical quality factor measured 300 in free vibration. Typical piezoelectric constant of the ZnO film was estimated approximately as 80% of single-crystal's value. The piezoelectric cantilever can be vibrated by applying the voltage with the frequency near the resonance to the piezoelectric layer. The excited amplitude per unit voltage at the resonance frequency was calculated as about 5 µm/V. The cantilever amplitude can be detected by measuring the current between electrodes, since the admittance depends on the quality factor. We have constructed a dynamic SFM without external oscillator and detector, and successfully obtained the surface images of a sol-gel derived PZT film in the cyclic contact operation mode. The longitudinal resolution of the SFM system was 0.3 nm at a 125 Hz bandwidth.

We experimentally studied the polarization mode dispersion (PMD) tolerance of an feed-forward equalizer (FFE) electronic dispersion compensation (EDC) IC in the absence of adaptive control, in 43-Gbit/s RZ-DQPSK transmission. Using a 3-tap FFE IC composed of InP HBTs, differential group delay (DGD) tolerance at a 2-dB Q penalty is shown to be extended from 25 ps to up to 29 ps. When a polarization scrambler is used, the tolerance is further extended to 31 ps. This value is close to the tolerance obtained with adaptive control, without a polarization scrambler.

We study effects of preamplifier nonlinearity on polarization mode dispersion (PMD) equalization performance of feed-forward equalizer (FFE) electronic dispersion compensation (EDC) IC. We have shown that a nonlinear limiting amplifier can be used as a preamplifier for FFE EDC IC for a 6-dB dynamic range.

A design scheme for a high-speed differential-input limiting transimpedance amplifier (TIA) was developed. The output-stage amplifier of the TIA is investigated in detail in order to suppress undershoot and ringing in the output waveform. The amplifier also includes a peak detector for the received signal strength indicator (RSSI) output, which is used to control the optical demodulator for differential-phase-shift-keying or differential-quadrature-phase-shift-keying formats. The limiting TIA was fabricated on the basis of 1-µm emitter-width InP-based heterojunction-bipolar-transistor (HBT) IC technology. Its differential gain is 39 dB, its 3-dB bandwidth is 27 GHz, and its estimated differential transimpedance gain is 73 dBΩ. The obtained output waveform shows that the developed design scheme is effective for suppressing undershoot and ringing.