Understanding Smart Sensors - Nomads.usp

Micromachining 33Table 2.4Comparison of Bulk, Surface, and LIGA Micromachining Processes (After: [20])Capability Bulk Surface LIGAPlanar geometry Rectangular Unrestricted UnrestrictedMin. planar feature size 2 × depth 1 mm 3mmSidewall features 54.74° slope Dry etch limited 0.2 mm runout over400 mmSurface and edge Excellent Mostly adequate Very gooddefinitionsMaterial properties Very well controlled Mostly adequate Well controlledIntegration with Demonstrated Demonstrated DifficultelectronicsCapital investment Low Moderate Highand costPublished knowledge Very high High LowElectroplated nickel overpressure stop by LIGA processPolysilicon diaphragmSiliconwaferFlowchannelMain cavitySilicon overpressure stopFigure 2.9 LIGA process combined with sacrificial etching for differential pressure sensor.(After: [21].)etching, and sidewall inhibitor ion-assisted anisotropic etching. Figure 2.10illustrates the different mechanical structures that result from these techniques.