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mosc_B_344 help

The ICCAP Instructions contain the basic procedures for making measurements and performing modeling. This screen is intended to point out things unique to using the mosc_B_344.mdl model file.

There are five types of capacitors in the mask set.:
  1. metal over field oxide with guard rings (A),
  2. metal over gate oxide (B),
  3. metal over field oxide (C),
  4. metal over diffusion 1 (D) and
  5. metal over diffusion 2 (E).
Each type has been implemented with 3 different geometries:

The square capacitor is 300 x 300 microns, the round capacitor radius equals 150 microns, and the finger capacitor has a center region of 100 x 100 microns and twelve 20 x 100 microns fingers.

Device Selection

Make the measurements on the round "B" capacitors. You can determine the doping level of the silicon from the capacitance measurements. Plug the result into the value for NSUB in the parameter set in the pmos3_344 model. You will also be able to determine the oxide thickness (Gate Oxide in the case of the "B" capacitors.)

Probe Assignments

These are metal oxide semiconductor capacitors (MOSC), and the ece344 textbook has a description of what the capacitance vs. voltage curves should look like, as well as some of the information that can be determined from them. Here are some brief highlights:
The Capacitance of the oxide is given by

Cox = dielectric constant of oxide * Area / Thickness

Under a particular bias polarity, a depletion layer will form in the silicon below the oxide, adding another capacitor in series with the oxide capacitor. The differential capacitance, Cd, of the semiconductor-space charge region is

Cd = dielectric constant of silicon * Area / Thickness of depletion region

The total capacitance is

Ctot = (Cox * Cd)/(Cox+Cd)

Here is a typical C-V curve for a MOS capacitor on a grounded n-type substrate with v_aluminum applied to an aluminum contact on top of the oxide. The flat regions corresponding to the oxide capacitance and the total capacitance at maximum depletion width are evident.

It is possible to model the capacitors by separating the capacitance into center and edge effects. The equations are similar to those used for modeling the p-n junction capacitance.
The total capacitance per area is

Ctotal = P * Cedge + A * Carea,

where P equals the perimeter and A equals the area. Note that the units of Cedge and Carea are pF/um and pF/um^2, respectively. By using two of the capacitors, it is possible to solve for P and A.

Save often!

ECE 344 home page.

This screen was created by Kevin Beernink - U of Illinois ECE Dept. -beernink@uiuc.edu
E-mail comments and suggestions to ece344@uiuc.edu or use the FEEDBACK FORM.
Software/ICCAP/moscB.help.html

Warning! This is the archived 1999 Fabweb site! Here is the latest site