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7 .
Now, we must send the code to the instrument . The simplest
method is to right-click in the open script window of TSB,
and select 'Run as TSP file' . This will compile the code and
place it in the volatile run-time memory of the instrument .
To store the program in non-volatile memory, see the "TSP
Programming Fundamentals" section of the Series 2600 Refer-
ence Manual .
8 .
Once the code has been placed in the instrument run-time
memory, we can run it at any time simply by calling the func-
tion 'FET _ Thres _ Search()' . This can be done by
typing the text 'FET _ Thres _ Search()' after the active
prompt in the Instrument Console line of TSB .
9 .
In the program '
FET_Thres_Search.tsp', the function FET _
Thres _ Search(vdssource, lowvgs, highvgs,
targetid) is created .
•
represents the voltage value on the drain-
vdssource
source of the transistor
•
represents the gate-source voltage low limit for
lowvgs
the search algorithm
•
represents the gate-source voltage high limit
highvgs
for the search algorithm
•
represents the target drain current for the
targetid
search algorithm
If these values are left blank, the function will use the default
values given to the variables, but you can specify each vari-
able value by simply sending a number that is in-range in the
function call . As an example, if you wanted to have the drain-
source voltage (V
) be 2 . 5 V, the gate-source voltage low value
DS
at 0 . 7 V, the gate-source voltage high value at 1 . 5 V, and the
target drain current at 2µA, you would send FET _ Thres _
Search(2.5, 0.7, 1.5, 2E-6) to the instrument .
10 .
The sources will be enabled, and the collector current of
the device will be measured . The program will perform an
iterative search to determine the closest match to the target
I
(within ±5%) . If the search is unsuccessful, the program
D
will print "Iteration Level Reached" . This is an error indicating
that the search reached its limit . Recheck the connections,
DUT, and variable values to make sure they are appropriate
for the device .
11 .
Once the sweep has been completed, the data (I
V
) will be presented in the Instrument Console window
DS
of TSB .
4.5.3 Program 11A Description
Initially, the instrument is returned to default conditions . SMUB,
which sources V
, is programmed as follows:
GS
•
Source V
•
1mA compliance, autorange
•
Local sense
SMUA, which sources V
the following manner:
•
Source V
•
Local sense
•
100mA compliance, autorange measure
•
1 NPLC Line cycle integration
Once the SMU channels have been configured, the sources values
are programmed to 0 and the outputs are enabled . The drain-
source voltage (V
function Check _ Comp(), and the program enters into the
binary search algorithm for the target drain current (I
the gate-source voltage (V
to the target I
tion counter is incremented each cycle through the algorithm . If
the number of iterations has been exceeded, a message to that
effect is displayed, and the program halts .
Assuming that the number of iterations has not been exceeded, the
data is displayed in the Instrument Console window of the TSB .
4.5.4 Modifying Program 11A
As written, the program sets the number of iterations to search for
target I
to 20 . You can change this by adjusting the l _ k _ max
D
variable to perform the iterative search as many times as is neces-
sary . Similarly, the allowed range for the I
Again, you can make this tolerance range as tight as necessary
by modifying the limits in line 155 . Note that reducing the target
range will probably require an increase in the number of itera-
tions as well .
4.5.5 Self-bias Threshold Test
Configuration
Figure 4-7 shows the general test configuration for the self-
bias method of threshold voltage tests . SMUB sources the drain
, V
, and
D
GS
current (assumed to be the same as the source current), and it
also measures the threshold voltage, V
arrange ment allows very rapid threshold voltage measurement
(milli seconds per reading) at very low currents, and it can be used
with both enhancement-mode and depletion-mode FETs . Note
that the high impedance sensing circuits and the floating capabili-
ties of the Series 2600 System SourceMeter instruments are key
characteristics that allow this special configuration to be used .
and measures I
DS
) is sourced, compliance is checked with the
DS
) value, measuring the I
GS
, and adjusting the V
value, if necessary . The itera-
D
GS
. SMUA sources V
T
SeCTIon 4
FET Tests
, is then configured in
D
) by varying
D
, comparing it
D
target search is ±5% .
D
. This
DS
4-7
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