Designing and building a prototype MEMS device with TSVs in it is pretty much unheard of. As Alissa Fitzgerald, Ph.D., founder and managing member of AM Fitzgerald &Associates explains it, TSVs don’t get introduced into a device until it’s in volume production, rather MEMS devices are developed with either a TSV or wire bond option. “Once the device is in mass production, you can think about sticking a TSV in it,” says Fitzgerald.
But that is all about to change, thanks to a partnership between AMFitzgerald, provider of engineering services for developing MEMS-enabled products, and MEMS foundry, Silex Microsystems. According to Fitzgerald, customers will be able have Silex’s standardized TSV integrated into their early stage prototypes.
AMFitzgerald provides full service engineering for customers throughout the entire MEMS development cycle, from concept evaluation to foundry transfer. The company relies on low-cost university facilities to build early stage prototypes for its clients, with an emphasis on improving design robustness and manufacturability for efficient transfer to foundry.
With certain MEMS applications, wirebonding is awkward. For example, for MEMS used in medical implant and catheters, where the catheter is only 2mm, using wire bonds takes extra real estate and creates packaging problem.. TSVs improve form factor, making the device easier to package.
“There’s a real need for this service,” explains Fitzgerald. “Up until now, customers developing image sensors and medical devices could only have TSVs in their roadmaps and could only try it at the foundry. It’s an expensive place to do process experience.” Additionally, many MEMS devices serve low volume niche applications, and don’t have volumes necessary to access TSVs at the foundry right away.
Silex’s Sil-VIA™ process involves a conductive ring that leaves a silicon core and is back filled with insulator material, enabling a conductive single crystal silicon interconnection. It’s a via-first process that can process at high temperatures. For MEMS devices, this is very useful because devices can be integrated on top of it without wafer bonding, explained Fitzgerald. This is important for the delicate structures of MEMS devices, which can be destroyed if the MEMS is processed first and the TSV formed afterwards.
“Sil-VIA™ has become a well established process in volume production at Silex for more than 5 years, and so we want to make it available to a broader audience,” explains Magnus Rimskog, sales director, North America, Silex, “When you’re focused on volume production, it’s sometimes hard for to work on projects that are exploratory studies rather than focused volume production set-ups and ramps. By working together with AM Fitzgerald we can now make the technology more accessible.”
For a new company developing a MEMS device, integrating a TSV that’s foundry-proven minimizes risk by testing the TSV early on, notes Fitzgerald. Additionally, the IC people will benefit, because the company can also use the service to develop custom interposers that can be used for rerouting s MEMS device to off-the-shelf CMOS when they have different footprints. So this is good news for both the MEMS and 3D integration communities.
