Power MEMS Development
Abstract
During this period, we began one short loop experiment to provide data for the flatness of the device silicon (Si) on the silicon-on-insulator (SOI) substrate. To complete this experiment, we processed one double-side-polished (DSP) and one SOI wafer using the same process as full wafer fabrication less the Metal 2, 4, and 5 layers. This process allows us to fabricate the cantilevers as Si-only cantilevers and verify they are flat before silicon dioxide (SiO2) growth or platinum (Pt) deposition. This short loop is still in process and will be completed at the end of the period. During this period, we began a repeat of the full wafer fabrication discussed in previous reports using one SOI and one DSP substrate. We also revised the process flow to include changes based on information gathered from the first full wafer fabrication and the finite element analysis (FEA) modeling results. These changes included a change of the heater material stack for the Task 1.1 circuit breaker and a change in the indent layer thickness. The SiO2 on the heater will be changed to silicon nitride (Si3N4), a tensile film that will cause a bending in the downward direction after release, opposite to the upward bend produced with the compressive SiO2. The increase to the indent layer will help keep the cantilever from touching the bottom substrate. We will begin processing wafers following this process flow by the end of the period. We set up an FEA model for the MEMS cantilever of the DC-DC switch and performed structural analysis using the model. The simulation result shows that the cantilever tip bends down for about 1 micrometer, considering initial film stresses of -350 MPa for the SiO2 layer and 100 MPa for the Au and Pt layers, as shown in Figure 1. This agrees with the experimental result. Thus, an increase of the indent layer thickness will help keep the cantilever tip from touching the bottom substrate after release.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 2009
- Accession Number
- ADA511507
Entities
People
- John Bumgarner
Organizations
- SRI International