Keithley Series 2600 User Manual

4-6
SECTION 4
FET Tests
SMUA, which sources V
DS
and measures I
D
, is then configured in
the following manner:
Source V•
Local sense•
100mA compliance, autorange measure•
1 NPLC Line cycle integration•
vdsbias • :10V
Following setup of both units, the outputs are zeroed and
enabled. SMUA applies the V
DS
bias, and SMUB begins the V
GS
voltage sweep. At each step in the V
GS
sweep, SMUA measured
the drain current (I
D
). The process repeats until all points in the
sweep have been taken.
Next, we encounter the part of the program where the transcon-
ductance values are calculated. Each transconductance value is
computed from ∆I
D
and ∆V
GS
. Finally, the data (V
GS
, I
D
, and g
fs
) is
printed to the Instrument Console of TSB. You can then copy and
paste the data to a spreadsheet to graph g
fs
vs. V
GS
and g
fs
vs. I
D
.
4.5 Threshold Tests
The threshold voltage (V
T
) is a critical parameter for FET charac-
terization, as well as process control. Basically, there are a number
of methods for determining V
T
, including several transconduc-
tance methods, the two-point extrapolated V
T
method, as well as
the V
T
@ I
D
search method. In this paragraph, we will discuss the
I
D
search method for finding V
T
, along with a self-biasing method
that takes advantage of the special capabilities of the Series 2600
System SourceMeter instruments.
4.5.1 Search Method Test Configuration
Figure 4-6 shows the general test configuration for the search
method threshold voltage tests. SMUB sources V
GS
, while SMUA
sources V
DS
and also measures I
D
. An iterative search process is
included in the program to allow you to enter a target I
D
value.
4.5.2 Example Program 11A: Threshold
Voltage Tests Using Search Method
Use Program 11A to perform the V
T
test using the search for target
I
D
method.
With the power off, connect a dual-channel System Source-1.
Meter instrument to the computer’s IEEE-488 interface.
Connect the test fixture to both units using appropriate 2.
c a b l e s .
Turn on the instrument and allow the unit to warm up for two 3.
hours for rated accuracy.
Turn on the computer and start Test Script Builder (TSB). Once 4.
the program has started, open a session by connecting to the
instrument. For details on how to use TSB, see the Series 2600
Reference Manual.
You can simply copy and paste the code from Appendix A in 5.
this guide into the TSB script editing window (Program 11A),
manually enter the code from the appendix, or import the TSP
file ‘FET_Thres_Search.tsp’ after downloading it to your PC.
If your computer is currently connected to the Internet, you
can click on this link to begin downloading: http://www.
keithley.com/data?asset=50919.
Install an N-hannel FET such as an SD210 in the appropriate 6.
transistor socket of the test fixture.
I
V
I
V
Series 2600
System
SourceMeter
Channel A
Sources V
DS
,
Measures I
D
Series 2600
System
SourceMeter
Channel B
Sets V
GS
for
Target I
D
V
DS
V
GS
Test
Fixture
FET
Under Test
Output HI
Output HI
Output LO
Output LO
I
D
Figure 4-6. Configuration for search method threshold tests

Keithley Series 2600 Specifications

General

Brand	Keithley
Model	Series 2600
Category	Measuring Instruments
Language	English