The presence of MEMS sensors such as the accelerometer and gyroscope in mobile devices is considered the norm. MEMS continue to be the mainstream technology that is capable of delivering sensors that are small, cost effective, and deliver better performance.
However, the shrinkage of available board space on a mobile device continues to put significant pressure on MEMS devices to be even smaller while adding more functionality, improved performance, as well as lowering the current consumption and at lower cost.
The MEMS and IC die continue to be fabricated on separate wafers. Integration of the two devices is either done on the die or wafer level, depending on the process integration. Novel techniques such as low temperature bonding to through-silicon vias come into play to help in size reduction and eliminate the need for package-level hermetic sealing.
Within a 1 mm thick packaged MEMS device, it is not uncommon to find between two to four chips stacked vertically. Considering starting wafers on 200 mm line is 725 um, there are significant challenges to reduce each chip to their appropriate thicknesses to conform to the 1 mm requirement. To make things more challenging, mobile phone OEMs are now seeking further reduction to less than 0.7 mm.
As the MEMS dies get thinner and smaller, the mechanical devices incorporated in them will obviously have less support structure. Design engineers have the daunting challenge to create new devices that are more robust and less immune to packaging and assembly stress.
These challenges of shrinking the MEMS device to enable OEMs to package more on the board forces the MEMS suppliers to continuously push the technology envelope in the arena of designs, process integration, and packaging.