Difference between Bulk and Surface Micromachining?
1 Answer
Sr No Bulk Micromachining Surface Micromachining
1 In this mechanical elements are fabricated by etching away the unwanted part in silicon wafer In this it is fabricated by building layers on layers
2 This creates structures inside a substrate This creates structures on top of a substrate
3 Larger structures are made with bulk micromachining It is difficult to build larger structures
4 Limited to low aspect ratio in geometry as surface dimensions are much greater than depth as height is limited by thickness of silicon wafer Not constraints by thickness of silicon wafer,so high aspect ratio geometries can be fabricated using surface micromachining
5 Straight forward and well documented process Complex masking design and production
6 Sacrificial layer is not required Etching of sacrificial layer is required
7 The process is less expensive but material loss is more The process is expensive but less material loss
8 Mechanical properties are superior Mechanical properties are good
9 Dimensional control is good Dimensional control is better
10 CMOS integration is fair CMOS integration is good
11 It causes a well known phenomenon in the micro electronics industry called undercut It does not causes undercut problem
12 Size is small Size is smaller
13 Typically uses wet etching techniques It uses dry etching techniques
14 Suitable for simple geometry such as thermal sensor,micro machined neuron wells Suitable for complex geometry such as micro valves and actuators
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