The emphasis on high aspect ratio micromachining techniques for microsystems/MEMS has been mainly to achieve novel devices with, for example, high sensing or actuation performance. Often these utilize deep structures (100-1,000 lm) with vertical wall layers but with relatively modest spatial resolution (1-10 lm). As these techniques move from research to industrial manufacture, the capital cost of the equipment and the cost of device manufacture become important, particularly where more than one micromachining technique can meet the performance requirements. This paper investigates the layer-processing costs associated with the principal high aspect ratio micromachining techniques used in microsystems/ MEMS fabrication, particularly silicon surface micromachining, wet bulk etching, wafer bonding, Deep Reactive Ion Etching, excimer laser micromachining, UV LIGA and X-ray LIGA. A cost model (MEMS-COST) has been developed which takes the financial, operational and machine-dependent parameters of the different manufacturing techniques as inputs and calculates the layer-processing costs at the wafer and chip level as a function of demand volume. The associated operational and investment costs are also calculated. Cost reductions through increases in the wafer size and decreases in chip area are investigated, and the importance of packaging costs demonstrated. R. A. Lawes (&)Optical and Semiconductor Devices Section,

A new process using photoresists as sacrificial layers has been developed to fabricate micromechanical components and systems. Commonly used photoresists are spun on a substrate as a sacrificial layer and patterned by a mask aligner. Free-standing metal structures are built by patterning a second layer of thick photoresist and electroplating on top of the photoresist sacrificial layer. Electrostatic microactuators and micromotors have been fabricated using the new photoresist sacrificial layer technique. Compared with all the existing sacrificial layer techniques, the photoresists used in the new process are easy to coat, easy to dissolve and less process steps are involved. The process is compatible with most of the materials and processes used in existing microfabrication technology. The fabrication of micromechanical systems becomes much simpler and cheaper with the use of a photoresist as a sacrificial layer.

A method of self-aligned, microcontact printing that avoids the need for dedicated alignment and stamping equipment is demonstrated. Complete miniature print engines combining elastically supported print heads with alignment structures that mate with corresponding features on etched substrates to allow mechanical registration are constructed from silicon parts. The impression can be transferred manually or using an in-built mechanism such as electrostatic actuation. 10 mm × 10 mm prototypes are fabricated using microelectromechanical systems technology, using a wafer-scale process based on deep reactive ion etching of either bulk silicon or bonded silicon-on-insulator wafers to form all mechanical parts and polydimethylsiloxane spray coating of etched surfaces to form soft stamps. Electromechanical characterization is performed and manual and electrostatic microcontact printing are both demonstrated through 1-hexadecanethiol ink transfer onto gold-coated surfaces over a 5 mm × 5 mm area with a minimum feature size of ≈2 μm.

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