In the data path circuits of asynchronous systems, logical faults may first manifest as undetectable, transient wrong codewords, in spite of encoding the inputs and the outputs and proper organization which enables the faults to be propagated to the primary outputs in the form of non-codewords. Due to this, the conventional methods of concurrent error detection (CED) using the logic (voltage) monitoring is not effective. In this paper, we suggest a mixed-signal approach to achieve CED for a class of asynchronous circuits, known as self-timed circuits. First, we show that it is impossible to guarantee the CED using logic monitoring of the primary outputs in spite of proper encoding and organization of self-timed circuits. Then, we discuss different manifestations of single stuck-at faults occurring during normal operation in these circuits. Finally, we present the feasibility of achieving CED using a built-in current sensor (BICS) along with encoding techniques.

Micromechanisms and actuators which are 10-100 micrometers in size are studied by research groups in universities, national research institutes, and private industries in Japan. Some of them belong to a "Micromachine Technology" project lead by MITI (Ministry of International Trade and Industries). Microfabrication technologies based on both IC-compatible processes and mechanical machining are under development. Application-oriented devices in automobile, communication and information industries are also investigated. The research goal is to build a smart micro system through the integration of moving mechanisms, sensors and electronics on a chip; this is the fusion of mechanics and electronics in the microscopic world. This paper reviews recent activities in MEMS research in Japan.

Micromachined sensors and actuators applied with electrostatic fields are getting widely developed. At the same time, "electrets," which are dielectrics carrying non-equilibrium permanent space charges or polarization distribution, are in demand because they improve the transducer characteristics. In this paper, we have reported on our successful fabrication of silicon dioxide electrets with extremely superior long-term charge stability by plasma chemical vapor deposition (PCVD). We have also reported on the correlation between the deposition conditions, the long-term charge stability and thermally stimulated current (TSC). Finally, the characterization of the long-term stable electrets will be described and discussed.

GaAs-based micromachining is a very attractive technique for integrating mechanical structures and active optical devices, such as laser diodes and photodiodes. For monolithically integrating mechanical parts onto laser diode wafers, the micromachining technique must be compatible with the laser diode fabrication process. Our micromachining technique features three major processes: epitaxitial growth (MOVPE) for both the structural and sacrificial layers, reactive dry-etching by chlorine for high-aspect, three-dimensional structures, and selective wet-etching by peroxide/ammonium hydroxide solution to release the moving parts. These processes are compatible with laser fabrication, so a cantilever beam structure can be fabricated at the same time as a laser diode structure. Furthermore, a single-crystal epitaxial layer has little residual stress, so precise microstructures can be obtained without significant deformation. We fabricated a microbeam resonator sensor composed of two laser diodes, a photodiode, and a micro-cantilever beam with an area of 400700 µm. The cantilever beam is 3 µm wide, 5 µm high, and either 110µm long for a 200-kHz resonant frequency or 50 µm long for a 1-MHz resonant frequency. The cantilever beam is excited by an intensity-modulated laser beam from an integrated excitation laser diode; the vibration signal is detected by a coupled cavity laser diode and a photodiode.

The optimal coding strategy for signal detection in the correlated gaussian noise is established for the distributed sensors system with essentially zero transmission rate constraint. Specifically, we are able to obtain the same performance as in the situation of no restriction on rate from each sensor terminal to the fusion center. This simple result contrasts with the previous ad hoc studies containing many unnatural assumptions such as the independence of noises contaminating received signal at each sensor. For the design of optimal coder, we can use the classical Levinson-Wiggins-Robinson fast algorithm for block Toeplitz matrix to evaluate the necessary weight vector for the maximum-likelihood detection.