PWS Analog Test

The Parametric Work Station™ (PWS) is a highly versatile analog IV tester with built in switch matrices combined with a suite of data log, graphing, analysis and programming tools in one portable, easy to use package.

PWS allows for measuring and analyzing:

the characteristics of semiconductor devices
the parametrics of digital device outputs and inputs (Voh, Vol, Vih, Vil, . . .)
analog devices including FETs, Bipolar transistors, Test structures, Op Amps, analog circuits
low resistance

and provides for:

stress measurement (ex. Hot Carrier Injection [HCI])
long term reliability testing
Flash memory cell evaluation
facilitation of parameter extraction
accurate on-wafer measurements

Modes of Operation

PWS can be operated interactively, “bench top fashion” through an intuitive front panel screen, or its operation can be automated using a built-in Visual BASIC compatible environment.

Further, these modes can be combined for powerful interactive diagnostics at user selectable breakpoints in an automated sequence. This is invaluable for test debug, or scrutiny of some measurement detail embedded in an extended test procedure.

Functions

Measurement Capabilities

The PWS SMU card has four highly accurate source/measure units (SMU), and two voltage-source/measure units (VS). Each SMU can force voltage while measuring current, or force current while measuring voltage. The VS’s can measure voltage and current while forcing a voltage. PWS can perform sweep measurement or discrete sampling measurement.

In addition to traditional DC force/measure, you can force an AC stress using PWS’s PULSE mode. In PULSE mode, user-selected SMU’s and VS’s are programmed to an initial value and then simultaneously pulsed to a different value for a programmed duration, with measurements taken at the end of the pulse. Pulsed measurements are useful when long exposure to certain bias conditions could cause parameter changes (e.g. due to heating).

The PWS also has a programmable SERVO feature wherein the current/voltage output of one SMU is driven based on the sensed current/voltage condition of a second SMU. A typical use of the SERVO feature is FET characterization where one SMU would be programmed to a DC voltage for DRAIN bias and a second SMU would drive the FET’s GATE voltage based on the sensed DRAIN current of the first SMU.

Guarded Switch Matrix Card

Switch Matrix cards consist of a 16 by 6 cross-point matrix of relay switches with each node separately switching a co-axial signal and its associated shield (guard). The matrix ties 16 external signals to an internal 6 wide buss connected to the SMU cards. The buss additionally provides for external connections to other instruments.

Expandable

PWS has expandable architecture and can be configured with any number of SMU and Switch Matrix Cards

Data, Plotting, Printing

Data logging uses a built-in Excel-compatible spreadsheet with automatic plotting in an embedded 2D-3D graphing tool. PWS allows you to store measurement setup and instrument setting information as well as measurement data.

High Speed Automated Test

PWS includes the VB rapid application developer (RAD) environment for the creation of test programs that include interactive operator screens. This gives you a powerful tool for automating testing in conjunction with the built-in switch matrix, for application such as wafer probe, stress testing, long term reliability testing, HCI, etc.

Analysis Function

Since data is stored in an Excel-compatible spreadsheet, functions can be created in the spreadsheet which analyze the raw data in any manner you need. As a simple example, you can create a column that calculates ‘gm’ or ‘hfe’ from other columns of logged raw data. Then you can add new plot tabs to graph the results of your functions. Functions are saved with the test setup and the results are automatically updated after new measurements are completed.

Also analysis of raw data can be performed using programmed BASIC algorithms when running in automation mode.

Remote Testing

PWS can control any external lab equipment via GPIB (IEEE488) by using remote control commands included in the VB environment.

Virtual Instrument Panel

PWS can be controlled interactively through the Virtual Instrument Panel shown below. All values defined in the Instrument Panel can be saved as an instrument setup.

The instrument panel is composed of three docked windows:

SMU Cards
Test Setup
Plot & Spreadsheets

SMU Cards Window

SMU Controls

SMU card modes and settings are controlled on the SMU Cards panel.

V / I
Use the radio buttons ‘V’and ‘I’ to set ForceV/MeasureI, ForceI/MeasureV, respectively.

Value
Use the ‘Value’ box to set static force values for the SMU. This value (along with all other conditions on the SMU Card panel) can be asserted immediately or as a terminating state in a sweep.

You can enter numbers in the value field in Scientific Notation (eg. 8.5e-2) or you can use engineering short-hand abbreviations (eg. 85m). Recognized abbreviations are listed below.

short hand notation	value
m	milli (x 1.0e-3)
u	micro (x 1.0e-6)
n	nano (x 1.0e-9)
p	pico (x 1.0e-12)

Limit
The ‘Limit’ specifies a protective limit that the SMU will not exceed.

DC / PulseTo
The radio buttons ‘DC’ and ‘PulseTo’ select the force and measurement mode for each unit.

In DC mode, specified conditions are asserted continuously when making measurements. If the unit is selected as the swept of stepped variable and in DC mode, the forced values are incremented in a staircase fashion with each condition applied for an internally defined settling time.

In PulseTo mode, conditions are set to a rest value and then pulsed to a different value for a programmed duration, with measurements taken at the end of the pulse. Immediately after each reading the forced values are returned to a ‘rest’ state. The rest time is determined by a duty cycle that you specify in Test Timing.

Measure

Sets current I-measure range. Use these dropdown list boxes to set the current measure range for each corresponding SMU. Typically you would use Auto range to allow PWS to determine the highest precision measurement. In situations where speed is critical and/or the expected range is limited, you can specify a fixed current range to achieve some improvement in measurement time.

Servo

Using the Servo feature, one SMU’s output can be Servo’ed until a programmed condition is measured at another SMU. This feature can be used to rapidly create conditions, such as driving a gate voltage to produce a desired drain current.

Test Timing

The contents of this panel vary depending on whether PulseTo mode is selected on any SMU.

Averages
Use to set the number of measurements to average to obtain each data point. Typically use more averages to eliminate noisy low value measurements.

60/50 Hz Reject
Use to average out 60 Hz noise.

Soak/Servo sec
Use to select the duration of the PulseTo, or the settling time for the Servo’ed SMU.

Duty Cycle
Determines the rest time for the PulseTo. For example, if you want to take a measurement every 1 msec with a 10% duty cycle, set a soak time of 100us and a Duty Cycle of 10%. (This produces a 100us pulse followed by a 900us rest.)

Test Setup Window – SWEEP

The Test Setup window of the instrument panel controls sweeps and measurements for the test. You can perform single sweeps by setting values in the VAR1 section. You can create stepped-sweeps by including VAR2 parameters.