|
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 |
Technique
Description |
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 |
|
|
| 
