An Introduction to mems (Micro-electromechanical Systems)

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Figure 21.  Surface micromachining of a cantilever beam using a sacrificial layer [2,3]. 

These layers (or thin films) are deposited and subsequently dry etched in sequence, with the 

sacrificial material being finally wet etched away to release the final structure.  Each 

additional layer is accompanied by an increasing level of complexity and a resulting difficulty 

in fabrication.  A typical surface micromachined cantilever beam is shown in Figure 21.  

Here, a sacrificial layer of oxide is deposited on the silicon substrate surface using a pattern 

and photolithography.  A polysilicon layer is then deposited and patterned using RIE 

processes to form a cantilever beam with an anchor pad.  The wafer is then wet etched to 

remove the oxide (sacrificial) layer releasing and leaving the beam on the substrate.  More 

complex MEMS structures can be achieved using structural polysilicon and sacrificial silicon 

dioxide, including sliding structures, actuators and free moving mechanical gears.  Figures 22 

shows the process flow for the fabrication of a micromotor by the commercially available 

Multi-User MEMS Process (MUMPS). 

The levels of complexity achievable with MEMS has already been shown in Figure 16.  In 

Ultra-Planar Multi-Level Technology (SUMMiT). 

The success of the surface micromachining process depends on the ability to successfully 

This step is responsible for curtailing the yield (percentage of the devices on a wafer that 

function properly) and reliability of fabricated MEMS due to the phenomenon known as 

Figure 22.  Surface micromachining of a MEMS micromotor using the Multi-

User MEMS Process (MUMPS) [30]. 

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