CMOS INVERTER LAYOUT TUTORIAL

Transcription

1 PRINCESS SUMAYA UNIVERSITY FOR TECHNOLOGY CMOS INVERTER LAYOUT TUTORIAL

2 We will start the inverter by drawing a PMOS. The first step is to draw a poly layer. Click on draw a rectangle and choose the poly layer PO from the right side pane. Use the ruler to get a poly rectangle of width= 0.1 um, and a length about 1 um as shown in the figure below. The second step is to draw a diffusion region. Draw a diffusion rectangle (DIFF) with a width of 0.48 um and a length of 0.9 um. Place the diffusion rectangle in the center of the diffusion area, that is, the diffusion area should be placed 0.4 um to the left and 0.4 um to the right of the POLY. The figure below shows the diffusion area placed. Place the diffusion area about in the middle of the poly as seen.

3 The next step will be placing a PIMP area. Place the area over the diffusion area having a margin area of 0.14 um taken from every corner as below. Each PMOS transistor should have an N-WELL base layer. Add a new N-WELL layer on your design. Take a 0.1 um margin from the bottom line. Stretch the N-WELL layer as seen below using the stretch tool found in the left toolbar. We will use this area in a couple of steps ahead.

4 Now add a metal area by choosing M1 from the right panel. The metal contact should be placed at 0.05 um from the right side of the diffusion and have a width of 0.23 um as seen below. Stretch the metal area down. Until now, your design should look like this

5 In the same manner add a new metal area on the left side and stretch it up as follow. Now place four contacts in the diffusion area as seen below. The contact should be at least 0.45 um away from the metal borders.

6 Now add a square NIMP area at the edge of the metal that you stretched upwards. Align the NIMP area to the PIMP rectangle as seen below. Add a diffusion area inside the NIMP square. And as before, take a 0.14 um margin from all the corners to place a diffusion area like this.

7 Now place a contact in the diffusion area as seen below. The contact should be placed as before, that is at least 0.45 um from the metal borders. This contact represents the source of the PMOS. You are almost done of designing the layout of your first PMOS. The design until now should look familiar as this one.

8 Now add a metal pin M1PIN on the source contact. Then press q on your keyboard and change the pin s name to the same name you used for your supply, for example AVDD. The pin should be placed over the contact as seen below. Now back to the original CMOS inverter circuit. As seen from the circuit, both gates of the NMOS and PMOS transistors Are connected together to form the input of the inverter. The gate of the MOS transistor is the POLY rectangle that we placed first. Thus the POLY of the PMOS will be stretched to meet the POLY of the NMOS and the PMOS drain which is represented by the metal rectangle that we stretched down should be in touch with the NMOS drain as seen from the circuit.

9 Stretch the POLY rectangle and add a place for a contact the will later represent the input pin as seen in the figure below. Now add a metal rectangle with the same size (0.21 um x 0.3 um) and this will represent the base of the input contact. After that add a contact using the same dimensions rules that we used earlier. Add an M1PIN over the contact and rename it to IN. This is the inverter s input signal.

10 After this, create the NMOS using the same steps that we used for the PMOS but with the following differences: 1- The Diffusion area s width is half that for the PMOS, that is 0.24 um. 2- Replacing the PIMP area with a NIMP area using the same margin rules. 3- No N-WELL layer surrounds the NMOS. The design should look like the one below. After that, start designing the source of the NMOS which will eventually be the contact at which the ground 0 volts is connected. This is achieved by drawing a 0.6 um x 0.6 um PIMP rectangle in which we place a 0.33 um x 0.33 um diffusion area. A contact along with an M1PIN called AVSS are placed using the same previous scheme. The design should look similar to this.

11 Now you have your complete design of your first inverter. But there is still one step to go. We need to define the output of out inverter. To do that, add an M1PIN on the common metal area between the two transistors. The M1PIN need not to be placed over a contact. Name the pin as the name you used in your schematic, for example OUT.

12 Here it is. Your complete layout design for your CMOS inverter. Verify your connections using the DRC test and then proceed with your simulations.