Introduction to MEMSPro

1. Introduction to MEMSPro EE485A Lab Exercise

2. MEMS Pro • Suite of modeling tools for designing MEMS structure • User enters masks and process flow • Software generates 3D model that can be used for finite element analysis • Can couple in “Technology Files” provided by different MEMS foundries. • Or can generate your own “technology file” for a custom process

3. MEMS Foundries • Execute a set process flow where users just vary the masks. • One example is PolyMUMPS • http://www.memscap.com/en_mumps.html • See slide show…

4. Executing a Layout in MEMSPro • We will now use MEMS Pro to create the mask set for a simple accelerometer that consists of a mass suspended with 4 tethers. • The capacitance between the upper electrode and lower electrode will be monitored to detect motion in the proof mass.

5. Open “MEMS Pro Launcher” from the START menu. • Within the launcher, select “Layout Editor” on the left, and hit “Run” • L-Edit will open up (there may be some stuff to initialize the first time) • Your screen should look like this:

6. Now let’s get oriented. Click on Setup -> Design to see some of the file defaults. • Under “Technology”, note that you are using a MUMPS technology file • Under “Grid”, note that the drawing units are microns, the snap is set to 1 mm and the major grid is at 10 mm. • For this project, set the snap to 5 mm, the major grid marks at 100 mm and the minor marks at 10 mm. • Hit “OK”

7. “substrate” is just for user convenience… not a real layer • Orientation to Layer Names “Poly0”, “Anchor1”, … “Metal” refer to mask layers in the PolyMUMPS process “HoleX” are pseudo layers that make it easier to create release holes in the structures. More on this later, ignore them for now.

8. Select Poly0 Select the “Drawing Box” tool in the upper left corner Draw a square on the grid. Select “Edit Object” from the “Edit” menu Set the dimensions as given on the right and hit “OK”. Zoom out using View -> zoom -> zoom to selections. Hit the ‘+’ and ‘-’ keys to see how to zoom in and out without going to the menus. Save your file to the desktop with the name “XYZ_MEMSProIntro.tdb” where “XYZ” are your initials. Creating the bottom electrode

9. Creating contact pads • Create a 140 um x 140 um square with its center at (745, -70) • Copy and paste the square on top of itself. Change the second copy so that it is in the “Anchor1” layer and has the dimensions of 120 um X 120 um, but with the same center. (Note that the middle mouse button is used to move a selection, also, view the object coordinates in center, dimension mode) • Repeat this process to create a square in Poly1 at the same location but with dimensions of 130 um X 130 um. • Repeat this process again to create a square in the Poly1-Poly2 Via layer that is 110 um x 110 um. • Repeat this process again to create a square in the Poly2 layer that is 120 um x 120 um. • Repeat this process one last time to create a square in the Metal layer that is 100 um x 100 um. • The result is a contact pad…

10. Copying and pasting the contact pads… • Now you will copy and paste the pads to where you need them in your design. • Select the entire pad structure, and hit ctrl-C then ctrl-V. Open the edit object window, and move the new center to (0, 815) • Repeat the process to place electrodes centered at (0, -815), (-815, 0) and (815, -815). • Now your drawing should look like this:

11. “Wiring” to the bottom electrode • Use rectangles to create a 100 um wide connection in Poly0 between the bottom electrode and the bottom right contact pad.

12. Creating the suspensions • Our suspensions (or springs) will be in “Poly1” • Draw a 500 um x 500 um with a center at (0,0) for the upper electrode • Draw a 20 um X 500 um rectangle that connects between the upper electrode and the “North” contact. (The bottom left corner is at (-10, 250)) • Repeat to create the suspensions to the “South,” “West” and “East” contacts.

13. Adding “heft” to the proof mass • In order to increase the proof mass size, we will also use the Poly2 layer for the center electrode. • Create a 490 um X 490 um box in the “Poly1-Poly2” via layer, centered on top of the electrode. • Create another 500 um X 500 um box in the “Poly2” layer on top of the electrode. • Now your structure is complete. • Save your file.

14. Developing the 3D Model… • Now go to Tools -> 3D Tools -> Edit Material Database to open the “Technology Manager” (or use the menu button which looks like a recipe card on the bottom left of the toolbar area) • Notice how the material properties are given for the layers in the PolyMUMPS process. • Go to the “3D Process Steps” tab and click through the process. • Select “Show Intermediate” and then say “OK”

15. Viewing the 3D model • Generate the 3D model using the “View 3D Model” button which is on the lower left corner of the menu bars. (Looks like binoculars in front of a cube). • MEMSPro will launch a window that describes the fabrication process, when it finishes, hit “Close Window” and you should see the start of the fabrication process. • Use the single right arrow to step through the process.

16. Play with the 3D viewer buttons… • Use the 3D model view buttons to zoom in and out and rotate the view. • In particular, take a close look at the points where the tethers connect to the proof mass. Notice the small steps that result from the layering process.

17. Predicting Behavior • Using the device dimensions and material properties (you should be able to find everything you need in your model), predict the following: • The mass of the “proof mass” • The spring constant for a single suspension. • The effective spring constant for all four suspensions. • The resonance frequency for the plate • The deflection of the plate for a 1g acceleration. • The deflection of the plate for a 10g acceleration. • The capacitance for the electrode structure without a force applied. • The capacitance for the electrode structure with a 10g acceleration. • Do you think that capacitance change is detectable?