Mr. Ekalak Chaowicharat Profile

Ekalak Chaowicharat

at Univ of New South Wales

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Proceedings Article | 28 February 2005 Paper

Fabrication of a nickel seismic mass microaccelerometer

Ekalak Chaowicharat, Chee Yee Kwok

Proceedings Volume 5649, (2005) https://doi.org/10.1117/12.581897

KEYWORDS: Photodiodes, Nickel, Diodes, Aluminum, Camera shutters, Microelectromechanical systems, Titanium, Semiconducting wafers, Scanning electron microscopy, Oxides

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In this paper, we present work on a surface micromachined opto-mechanical microaccelerometer employing Ni seimic mass. The device uses optical detection to sense motion. The microaccelerometer consists of a 500 um x 500 um electrodeposited nickel suspended by a folded beam spring on each corner over 10 pairs of 30 um x 400 um rectangular photodiodes. The seismic mass also has an array of rectangular holes parallel to the photodiodes. Each hole partially exposes a pair of adjacent photodiodes to to be illuminated by an LED. Once the mass experiences acceleration, it will act as a mechanical shutter and alters the amount of exposed area of photodiodes. For each pair of the photodiodes, as the shutter moves, it will increase the exposed area of one diode and at the same time will at the same time reduce the exposed area of the other diode by the same amount. Fully differential current signals can then be taken by appropriately biasing the photodiodes. By using differential sensing arrangement, the effects of noise and dark current can be reduced significantly. The microaccelerometer is tested on a rotating disc. The frequency response of the accelerometer is relatively flat up to 1500 Hz, then, it rise sharply at resonant frequency of approximately 1700 Hz. An open loop sensitivity of 9.2mV/g in the direction of acceleration is obtained. Cross axial sensitivity was below the noise level.

Proceedings Article | 29 September 1999 Paper

Silicon surface micromachining over active devices

Ekalak Chaowicharat, Chee Kwok, Graham Rigby

Proceedings Volume 3891, (1999) https://doi.org/10.1117/12.364441

KEYWORDS: Microelectromechanical systems, Annealing, Oxides, Aluminum, Tungsten, Photodiodes, Silicon, Semiconducting wafers, Metals, Surface micromachining

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Reported modification of CMOS processes to incorporate MEM structure require the structure to be located outside the active area. This paper describes the fabrication of microstructures directly over active devices rather than alongside them. Several issues need to be addressed with this fabrication process. The first issue is the choice of the metal to be used for metalization. Aluminium is no longer a viable option as some of the post-metalization processing steps exceed its melting point. Tungsten and titanium are the alternative candidates with sufficiently high melting point and low resistivity. The second issue is the non-planar surface profile across the wafer after the fabrication of the active devices. The sacrificial layer must be greater than the surface profile across the wafer and furthermore planarization of the sacrificial layer is necessary before the structural layer is deposited or electroplated. The final issue is post-metalization process temperature considerations for stress relaxation where either rapid thermal annealing or a relatively low temperature annealing of the microstructure is carried out. In this paper, these issues will be addressed, using the processes developed for the fabrication of an opto- mechanical microaccelerator as an illustration.

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