Crableg Resonator Tutorial (Part 1) | |||
From Design to Testing | |||
Purpose of this document This tutorial provides an overview of the series of steps from the design of a crableg resonator through the testing of the same bonded die. The second part of this tutorial (Part 2) will focus on testing the bonded die using the MIT Microvision system. As such, it may serve as a reference for new users in learning the system. Data collected on a crableg resonator die at Carnegie Mellon is detailed in Part 3. Background
Designing a properly functioning MEMS device has become increasingly more complicated as the layouts have become more complex. Few people have the time or money required to wait for a design to be fabricated to then realize a mistake was made in the layout causing thier device to not work as they intended, or to not work at all. Time and effort invested in design can help save time, and money,in the end.
Design includes hand analysis, simulation, and layout. Hand analysis invloves first order calculations and average values. Simulation utilizes software to factor in second and higher order effects. Carnegie Mellon's NODAS is one such simulation tool. Layout may be done by hand, utilizing p-cells, or even auto-generated from a simulation schematic.
After the design is included on a fabrication run, the die will be returned a few months later from the foundry. After the necessary post-processing steps, the die is ready to be tested. The MIT Microvision system is one of many instruments that can be used for testing. This system optically measures the motion of a MEMS device in the x, y, and z planes. Bode plots of the response can identify the resonant frequency and other properties of the device.
Comparision of the simulation and test results can indicate the accuracy of the simulation. The simulation most likely will need to be redone with the actual device dimensions which may be slightly different than the layout dimensions.
This tutorial will follow through these steps for a simple crableg resonator test structure.
Hand Analysis Hand analysis, sometimes referred as 'back of the envolope' calculations, utilizes first order calculations and average values to characterize the performance of a device. A few hand calculations for a crableg resonator may include the spring constant, the force generated by the comb drive, AC displacement amplitude, DC displacement amplitude, resonant frequency, and quality factor. A few of these calculations are shown here in PDF format. Simulation
Carnegie Mellon's NODAS was used to simulate and automatically generate the layout for this crableg resonator. NODAS divides a MEMS device into a few simple components - beams, plates, comb drives, etc. The first step is to build a schematic of the device as shown here. Layout
The last item needed is a layout of the design. NODAS has the ability to automatically generate the layout from the schematic that we built. The automatically generated layout is shown below. This layout would be instantiated on a chip and connected to bond pads. |