The progress of the wireless transceiver industry has been shaped by both cost and size consideration, with RF/IF bandpass filters competing for space and function at the board-level. Methods to appease these restriction have focused on removing the IF filter and placing more of the load on the circuit complexity and performance, which could be detrimental in future expansive endeavors. High-Q RF filters must be improved to allow for next generation wireless architectures without the size and cost penalties seen in the past.
Researchers at University of Michigan have developed a new location dependent laser trimming technique of tuning the frequency of micro scale clamped-clamped beams (“CC-beam”). Previously used methods could only precisely tune resonators on the macro-scale (mm to cm), but these methods could not accurately trim on the micro-scale (um) without creating stress distributions. At the center of a CC-beam, negative frequency shifts are as low as -22 ppm, but by moving the trim location off center frequency shifts increase to a maximum of -28,400 ppm. Beyond this point, frequency shifts turn positive. Unfortunately, on the micro-scale, these off-center trims cause stress distributions that can reduce the Q by about 25 percent. However, using this new method of selecting the next trimming point at a mirror symmetric location of the previous off center point restores the original Q value.
Applications and Advantages
- MEMS resonators and filters
- Micro-scale trimming capability-nl-with CC beams