Novel design and fabrication of a MEMS heater

Purpose:

v Create a MEMS device which is capable of generating an appreciable amount of heat

v Learn about the design and fabrication of MEMS devices

Goals/Responsibilities:

• Designing a MEMS heat sealer which was capable of bonding two pieces of polyethylene (PET) together, creating a hermetic seal
• Coming up with a fabrication plan to support these designs
• Create a heater which can reach a temperature which would cause it to glow
• Create a heater capable of reaching a temperature suitable for heat sealing plastic
• Utilize a single mask design, which greatly increases ease and success of manufacturability in an R&D environment

The substrate material to be used was PET which had been previously coated with Indium Tin Oxide (ITO) and then with a negative dry film resist. My designs can be seen below in Figure 1.

 Figure 1. CAD drawing of ITO heat sealer design

These designs were intended to be made into photomasks for photolithography, so they had to be modified to fit the standards of the printing shop. They were taken out of SolidWorks and brought into DraftSight, where each design was modified and duplicated to fill a 100mm wafer as seen below in Figure 2.

Figure 2. DWG format drawing of the two heat sealer designs

The ITO heaters were fabricated using standard photolithography processes. Since the ITO/PET came already coated with the dry film photoresist, it was able to be processed using a mask aligner immediately. After exposing the resist, a 1% sodium carbonate solution was used to develop the pattern, and a 5% hydrochloric acid solution was used to etch the ITO. Finally the resist was stripped, and the heaters were tested. A video of the device operating can be seen below.

Figure 3. ITO heater heating and cooling

As the video demonstrates the heaters have a very fast response time, the element reached full temperature within approximately three seconds. Unfortunately the maximum temperature the heater reached was only about 130°C, at approximately 30V. However, the heaters appeared very robust, and could have reached a higher temperature with a higher applied voltage.

The other design was implemented in aluminum on silicon and can be seen below in Figure 4. To fabricate these devices, bare silicon wafers were sputter coated using an aluminum target, spin coated with S1818 photoresist, patterned using a mask aligner, developed, and wet etched.

Figure 4. Heaters etched in aluminum on silicon being tested

These heaters appeared to achieve a much lower temperature, although we are not confident of the measurements from the FLIR IR camera.

Figure 5. FLIR IR camera image of aluminum heaters with 30V applied

These devices were also measured using an interferometer. We were able to verify that the traces were properly formed and the dimensions were within specification.

Figure 6. Interferometer data regarding trace depth and size