Hints, Tips and Solutions


Volume 11, Number 10, October 2000

Q. How can I measure CJSWG (CJGATE) Capacitance using UTMOST III ?

A. For the UTMOST III versions greater than 17.2.0.R, the UTMOST users can measure the CJSWG (CJGATE) capacitance using the "CJ/CJSW" routine.

The CJ/CJSW routine in MOS technology has been modified to measure the CJSWG (Peripheral portion of the junction capacitance under the gate) capacitance.

In order to extract the additional CJSWG capacitance there should be three structures available in the test die:

  1. The Area structure (typically a large diode). Used to extract CJ

  2. The Periphery structure (finger structure, periphery maximized). Used to extract CJSW

  3. The Gated diode structure. This structure could be a MOS transistor with very large width. Used to extract CJSWG.

The area and periphery values of each diode should be entered into UTMOST's "Device Pads Screen". In order to open the "Device Pads" screen press the "Hardware"button from the main UTMOST screen and select the "Probing" menu option. Then press the "Devices" button. (Figure 1).

Figure 1. Device Pads screen with three structures'.
Area and Periphery values entered.

In addition to the Area and Periphery values, the width of the region which remains under the gate should be entered for the CJSWG structure. The gate width value of the CJSWG structure can be entered under the "Width" column of the "strategy"screen. The CJ and CJSW structures do not require any "width" or "length" value entered in the strategy screen. They can be left blank as long as their total area and periphery values are given in the "Device Pads Screen". The Periphery of the CJSWG structure should not include the under the gate side of the diode. It should only include the sides which are not under the gate.

To measure the third structure (CJSWG) the "CJSWG_measure" flag in the Set Measurement screen of the CJ/CJSW routine should be set to "1". After the flag is set to "1" the user can proceed with measurement and parameter extraction. The system will prompt the user with messages to connect the proper structures before each measurement. After the data collection the standard UTMOST III "Fitting"and "Optimization"procedures can be applied. (Figure 2.)

Figure 2. CJ/CJSW routine measured and simulated
curves including the CJSWG data.

If there is no CJSWG structure available and only CJ and CJSW values need to be extracted, then the "CJSWG_measure" flag should be set to "0".

The total capacitance of the CJSWG structure will be calculated as :

CJtotal = CJ x Area3 + CJSW x Periphery3 + CJSWG x Width

Area3: Total area of the CJSWG diode.

Periphery3: The Periphery of the CJSWG diode excluding the "under the gate" portion.

Width: The width of the region which remains under the gate.


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