Objectives: This week, we will become familiar with the CAD tools that are available to design the masks used  to fabricate our projects. To do your own microstructure design, you will have to prepare your own masks! The masks used in the class were designed by Dr. Norman Sheppard.

1. Browse the web page for last year's project and read the final report by T. Edwards.

2. Download the files PXMask.tdb and PXMask.cif  from the anonymous ftp site: olympus.ece.jhu.edu the directory /pub/courses/495. Login as anonymous and type your name as the password. Note that the .tdb file is a binary file so make sure that you have binary transfer turned on when using ftp. 

3. Place the two files on a diskette.

4. Alternatively, you can click on the each of the two files and  when prompted save the files on your diskette.

II. Lab Work:

The CAD program LEDIT will be used for mask layout and editing. This  can be found in the Computer  Engineering Laboratories in Latrobe Hall.  The program runs under Windows 98 and there will be instructions of how to login and work with the program on the computers designated "LEDIT". Make sure that you change the color resolution of the computer for 256 colors (it is probably setup for millions).

Question 1: Start the program and load the file PXMask.tdb You will see the various structures that make up the MEMS pressure sensor because they are coded by different colors and patterns.

The diffusion mask patterns are green, the metallization mask patterns are blue, the contact cuts are black and the membrane etch mask is coded by purple grid pattern. The design is done hierarchically and you can navigate through the individual cells. If you make changes in a leaf cell, these changes will manifest themselves to all instances of the leaf cell. As our lab facilities are limited the number of mask steps  are also limited. A typical CMOS process has a minimum of nine mask layers and more advance processes will have eleven or twelve.

The design is done on a grid and the size of the basic grid spacing is one lambda. This is a parameter that depends on the process. For example, state of the art CMOS processes today have a lambda of 0.15 micron.

Question 2: Calculate the dimensions of all structures on the mask. Get a hardcopy of the design by printing it and indicate on it these dimensions. What do you think lambda is for our process.

Question 3: Modify the basic cell ( called MicroDevice ) that is replicated 16 times, to change the design from what is on the wafer now, a  pressure sensor,  to what you did in the class, an interdigitated wire pattern.  Do not erase the alignment marks or the test patterns on the die. Note how as you change the single cell all the cells in the array are modified. Export the file into a .cif format.

Congratulations! You have just created your own mask design.

III. Postlab Work:

1. Check out MOSIS (Metal Oxide Semiconductor Implementation Service), a silicon foundry that provides services for state of the art IC processes. What is the  state of the art fabrication process offered by the foundry today? How many metal layers and how many polysilicon layers are offered in this process?
2. Explore on the WWW and report on other foundries, available specifically for Microelectromechanical Systems (MEMS). What are the specifications of the processes offered by these foundries?
3.