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Draw and explain working principle of cantilever. Show basic quantitative behavior of cantilever. Also discuss process steps for fabrication of cantilever.

Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 10M

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Surface micro-machined devices are typically made up of 3 types of components.

1. A sacrificial component [spacer layer]
2. A micro structural component
3. An insulator component

The sacrificial components are usually made of phosphosilicate glass [PSG] ori $Sio_2$ deposited on substrates by LPCVD techniques

PSG can be etched more rapidly than $Sio_2$ in HF etchants. These components in the form of films can be as long as 1 to 2000 $\mu m$ and 0.1 to 5 $\mu m$ thick.

Both micro-structural and insulator components can be deposited in thin films. Polysilicon is a popular material

The etching rates for sacrificial components must be much higher than those for the two other components.

1. - A silicon substrate base with a PSG deposited on its surface.

2. - A mask [ mask 1 ] is made instep 2 to cover the surface of the PSG layer for the subsequent etching to allow for the attachment of the future cantilever beam as shown in step 3.

4. - Another mask [ mask 2 ] is made for the deposition of poly-silicon micro structural material in step 4.

The PSG that remains in step 5 is subsequently etched way to produce the desired cantilever beam as shown in step 6.

The most suitable etchant used in the last step for the sacrificial PSG layer is 1 : 1 HF, Which is made of 1 : 1 HF : $H_2O$ + 1 : 1 HCI : $H_2O$

After itching, the structure is rinsed in deionized water thoroughly followed by drying under infrared lamp.