Kuniki Ohwada

A micromachined vibrating rate gyroscope with independent beams for the drive and detection modes

We investigated the mechanical coupling between the drive and detection modes of micromachined vibrating rate gyroscopes, and designed and fabricated a gyroscope with a new structure to reduce the coupling. The coupling of the oscillator was measured using a new measurement system with a two-dimensional laser displacement meter. The oscillations were found to have an elliptical motion due to the coupling. When the frequency mismatch was reduced by means of electrostatic frequency tuning with a DC bias voltage, the coupling increased. The new structure, which has independent beams for the drive and detection modes, exhibited weaker coupling; and the resolution was 0.07°/s at a band width of 10 Hz.

A micromachined vibrating gyroscope

Abstract A vibrating microgyroscope with a thin polysilicon resonator fabricated by silicon surface micromachining is described. The 400 μm × 800 μm resonator is driven in a lateral direction by electrostatic force, and the angular rate is detected as the capacitance change between the resonator and its substrate. Mechanical Q -factors for the driving mode and the detecting mode of the polysilicon resonator are 2800 and 16 000, respectively, at pressures below 0.1 Pa. Methods are presented for modifying the difference between the resonance frequencies of the driving and detecting modes. The test device shows a noise-equivalent rate of 2° s −1 .

Characterization of piezoelectric properties of PZT thin films deposited on Si by ECR sputtering

Abstract Ferroelectric lead zirconate titanate (PZT) thin films are deposited at a low substrate temperature (530–590 °C) by an electron cyclotron resonance (ECR) sputtering method using two targets: a ceramic PZT and a lead metal target. Si wafers are employed as substrates. The piezoelectric constant e31 is 2.1 C m−2 without poling treatment for a PZT film deposited at 550 °C.

Uniform groove-depths in (110) Si anisotropic etching by ultrasonic waves and application to accelerometer fabrication

Abstract The use of ultrasonic waves to obtain uniform groove depth in (110) Si anisotropic etching has been studied. Using dynashock-type ultrasonic waves, the frequency of which is switched between three frequencies at very short intervals, grooves with uniform depth can be successfully formed with widths of 1–20 μm independently of pattern width and pattern spacing. This technology is applied to the fabrication of an accelerometer with comb-type narrow-gap electrodes. Comb electrodes with a minimum gap of 3.0 μm and a height of 58 μm can be formed uniformly, although they have different pattern widths and pattern spacings. The capacitance of this device has a high sensitivity to acceleration of 39 pF g-1. By combining it with an output CV converter and amplifiers, we have produced a sensor with good full-scale linearity of 0.63% over the acceleration range 0 to + 2g.

Anodic bonding of lead zirconate titanate ceramics to silicon with intermediate glass layer

Abstract Anodic bonding was investigated for bonding lead zirconate titanate (PZT) ceramics to silicon wafers. Sputtered borosilicate glass was used as an intermediate layer. Well-bonded wafers were obtained by applying voltage of 300 V at 500 °C or 500 V at 400 °C. The bonded area increased while applied voltage was kept constant. The size of the bonded area depended on the resistivity of the ceramics at bonding temperatures. A cantilever was made with a PZT-Si bonded wafer, and its basic operation exhibited potential usefulness for application to microsensors and microactuators.