Technology: Dissolved Wafer Process

To fabricate MEMS devices, ISSYS uses the dissolved wafer process (DWP) as its core technology because:

  • ISSYS has secured exclusive licenses to patents covering the DWP process from the University of Michigan.
  • ISSYS possesses deep expertise in this process and has developed substantial intellectual property in both patents and trade secrets that compliment the original DWP technology created by the University of Michigan. In addition to ISSYS' in-house expertise in DWP, ISSYS Cofounders Dr. Ken Wise and Dr. Khalil Najafi continue to assist ISSYS team members as needed in resolving complex technical problems.
Thousands of ISSYS medical pressure sensors on a 4" wafer created using DWP

DWP combines the advantages of both surface and bulk micromachining (see table), including:

  • Allows for simple, single-sided wafer fabrication processes
  • Yields reproducible and accurate process steps
  • Produces high aspect ratio monocrystalline silicon microstructures
  • Accommodates both thick and thin microstructures on the same chip
  • Produces high density microstructures for a variety of sensors and actuators
Dissolved Wafer Processing Steps

Advantages of Dissolved Wafer Process Relative to Bulk and Surface Micromachining
MEMS Techniques* Dissolved Wafer Processing Bulk Micromachining Surface Micromachining
Entails creating structures inside of a silicon wafer with boron diffusion. The wafer is then attached to a substrate, and the non-Boron-doped portions of the wafer are dissolved, leaving a device created from the structures that were built into the wafer. Involves using techniques to directly etch structures into the silicon wafer. This etching can be done selectively using parameters such as crystal orientation, doping concentration, and the presence of other materials such as silicon oxide. Consists of building up and patterning successive layers of sacrificial and mechanical layers on the front-side of a silicon wafer to create structures. The sacrificial layer is then removed, leaving freestanding polysilicon mechanical components.
Single-sided wafer fabrication process  
Reproducible and accurate process
Mono-crystalline silicon microstructures  
High aspect ratio devices  
Thick and thin microstructures on the same chip  
High density microstructures (number on a single wafer)
High Density
Low Density
Highest Density
Versatile (variety of sensors, actuators, & microstructures)  
Potential biocompatibility for chronic implanted applications  

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