Low-cost MEMS fabrication using injection molding

December 28, 2012 – Researchers in Japan have devised a microelectromechanical system (MEMS) fabrication technology using printing and injection molding, fabrication of large-area devices with low capital investment, without a vacuum process, and lower production costs. Thus, MEMS devices can be made and applied for fields where manufacturing cost has been an issue, such as lighting.

The team from the Research Center for Ubiquitous MEMS and Micro Engineering of the National Institute of Advanced Industrial Science and Technology (AIST) integrated microfabrication technology and MEMS design evaluation technology, and combined it with Design Tech Co. Ltd.’s signal processing technology to fabricate a lighting device.

Conventional commercial MEMS devices use fabrication techniques with semiconductor manufacturing systems used to produce integrated circuits, including vacuum processes. Resins could be used to form patterns onto moving microstructures but production costs are high due to vacuum-based processes. Also, it has proven difficult to form and thin MEMS structures such as springs and cantilevers because resins harden immediately after mold injection.

AIST researchers now say they have realized low-cost printing and transferred the structure using injection molding, and improved the mold structure to fill thin moving structures. A film for transferring the MEMS functional laser is formed, and the release layer and MEMS functional layer are printed onto the film with a screen or gravure printer. The printed film is aligned and put into an injection mold, into which is injected a molten resin that is cooled and solidified into the MEMS structure. The mold is then opened and the MEMS structure is separated from the film; the ink layers printed on the film are transferred to the MEMS structure.

Figure 1: MEMS fabrication processes by printing and injection molding.

The printed MEMS functional layers can be changed according to the desired purpose of the MEMS device — from acceleration sensors and gas sensors to power generation devices. This enables low-cost MEMS fabrication in fields where costs are currently too high. One example the AIST highlights is in light distribution control of LED lighting. MEMS mirrors produced with semiconductor manufacturing processes are based on costs determined by devices per wafer; so large-area mirrors are costly, while more cost-friendly micromirrors necessitate a more complex optical system. This new MEMS fabrication technology, though, could produce low-cost large MEMS devices (larger than several mm across), which opens the door for MEMS-based active light distribution control devices. Future work will seek to improve the symmetry of the MEMS mirror synchronization with the LED timing, and expand the range of the light distribution by improving the arrangement of the optical system, the signal processing, and the control circuit.

Figure 2: MEMS mirrors for active light distribution fabricated by using only printing and injection molding (left), and examples of the resulting light distribution patterns (right).

Injection molding can be used easily to form complex 3D objects such as spheres; the researchers expect MEMS devices will be formed on the surface of, or inside, 3D objects. Moreover, injection molding processes are commonly available in Japan, and systems cost less than semiconductor manufacturing systems. AIST projects its work will lead to MEMS fabrication coming out of non-semiconductor industries, such as plastics molding — and participation from these other sectors into MEMS manufacturing will help develop new applications for MEMS devices.

Figure 3: Examples of MEMS devices fabricated with the AIST technology. Top & middle: A reflective mirror and a mirror displacement sensor incorporated into a MEMS mirror device for lighting. A mirror ink for the reflective mirror, a conductive ink for the strain sensor, and a magnetic ink for driving the mirror are printed on the film, and then the printed ink patterns are transferred to the MEMS structure by injection molding. The MEMS mirror device for lighting did not break after more than 100 million operations driven by an external coil. Bottom: A MEMS device array can be fabricated using an arrayed MEMS pattern mold.


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