Appendix A: Overview of the HP4145A Parameter Analyzer
“Intelligent Instrument Streamlines dc Semiconductor Parameter Measurements” Hewlett-Packard Journal October 1982 Volume 33 • Number 10 • p 3-14. by Kochichi Maeda, Jin-ichi Ikemoto, Fumiro Tsuruda and Teruo Takeda [This document directly excerpts portions of a publication concerning the HP 4145A of interest to students in ECE 549. – ed] The Hewlett-Packard 4145A Semiconductor Parameter Analyzer is a powerful tool designed to make measurements on transistors and diodes. The 4145A has a built-in microcomputer and can automatically execute measurements and calculations. Two markers on the display can be positioned and the slope displayed on the screen. In stand-alone use the 4145A can evaluate parameters such as threshold voltage (Vt), transconductance (gm), common-emitter current gain (hFE), Early voltage (VA) and others. A.1 Features Some of the features of the 4145A are: Four stimulus/measurement units that can be programmed to perform in one of three different modes: 1. Voltage source and current monitor (V mode) 2. Current source and voltage monitor (I mode) 3. Common connection (COM mode). Two voltage sources (VS) that can be linearly or logarithmically swept over their programmed output range. Two voltage monitors (VM). Two user functions that allow front-panel programming of two different arithmetic operations for calculating parameters from measured values. The results can be displayed in real time versus the measured values. A.2 Hardware Architecture A block diagram of the 4145A’s hardware system is shown in Figure A.1. The digital system is functionally divided: the measurement section is coupled to the rest of the digital system through an optoisolator. The SMU controller has intelligent functions that enable the system processor to give commands or get data with ease. For example, it has sweep control capability. Once the SMU controller has been given sweep parameters (linear/log, start value, step size, number of steps), it sets up the source output values, gives hold or delay time, measures monitored values and reports measurement data automatically at every step.
A.1
Appendix A: Overview of the HP4145A Parameter Analyzer
Figure A.1 Block diagram of the 4145A’s hardware system consisting of a grounded digital section and a floating measurement section. Communication between the two sections is through an optoisolator. A second feature is the line-frequency-synchronized sampling and averaging technique to reduce ac line noise. When INTEG TIME is set to SHORT, the measured data is stored directly without integration. However, when INTEG TIME is set to MED, 16 samples are taken during one ac line frequency cycle and averaged for each measurement value. The LONG setting averages 256 samples taken during 16 ac line cycles. The sample timing is controlled by a timer that counts the main processing unit clock pulses. A.3 Typical Applications of the 4145A Semiconductor Parameter Analyzer Two examples evaluate a MOS device. Part (a) of each figure is a hard copy of the 4145A’s graphic display and part (b) shows the 4145A test connections and SMU mode settings to the device under test. A.4 MOS Threshold Characteristics The five curves shown in Figure A.2 represent a MOS device’s characteristics at five different substrate voltages VSB. The threshold voltage Vt of an enhancement-type MOSFET is defined as the gate voltage required to cause a predetermined value of drain current (in this example, 10 µA). Vt can be obtained by moving the display marker along the curve until ID = 10 µA (point A), and then reading the value VG at that point as displayed numerically above the graph. In Figure A.2, VTO VSB 0 is 2.213V. A.5 Threshold Voltage Another method of measuring Vt is to bias the MOSFET such that the gate and drain are always at the same potential and measure the characteristics in the saturation region. Drain current in the saturation region is calculated as
I D VGS - Vt
2
(A.1)
A.2
Appendix A: Overview of the HP4145A Parameter Analyzer
Figure A.2 (a) Log-linear display of MOSFET threshold characteristics for five different substrate voltages. (b) Source setup values and test configuration for (a). where β is the gain factor of the device. By taking the square root of this equation, we find that the relationship between I D and VGS is linear, the slope of the line is , and the point at which the line crosses the X-axis is Vt. Thus
I D VGS Vt
(A.2)
Figure A.3 (a) Linear display for determining threshold voltage of an MOS device (see text). Cursor is at point A, marker at point B. (b) Source setup values and test configuration for (a). The 4145A’s user function can be set up to perform this calculation during the measurement. From Figure A.3, X-INTERCEPT shows a Vt of 2.17 V. The square of the line GRAD is 566 10 6 .
A.3
Appendix A: Overview of the HP4145A Parameter Analyzer The four stimulus measurement units are the heart of the 4145A. Each SMU can be programmed to function as a voltage source and current monitor (V mode) or a current source and voltage monitor (I mode). In the V mode, an SMU can supply from ± 1 mV to ± 100 V over three output ranges as given in Table A.1. In the I mode, currents as low as 1 pA and as high as 100 mA can
Table A.1 SMU Operation Capability: V Mode Voltage Range ± 20 V ± 40 V ± 100 V Maximum Current Io 100 mA 50 mA 20 mA
Resolution 1 mV 2 mV 5 mV
Accuracy ± (0.1% of reading + 0.05% of range + 0.4Ω x Io)
Io = output current at set voltage
Table A.2 SMU Output Capability: I Mode Current Range
± 100 mA
Resolution
100 μA 10 μA 1 μA 100 nA 10 nA 1 nA 100 pA 10 pA 1 pA
Accuracy
±[0.3% of reading +(0.1+0.002Vo)% of range]
Maximum Voltage Vo
20V (I≤100mA) 40V (I≤40 mA)
± 10 mA ± 1000 μA ± 100 μA ± 10 μA ± 1000 nA ± 100 nA ± 10 nA ± 1000 pA
±[0.5% of reading +0.1+0.002Vo)% or range] ±[5pA +1% of reading +(0.1+0.002Vo)% of range]
100V (I≤20mA)
Vo = output voltage at set current
be forced as listed in Table A.2. If higher currents or voltages are required, an SMU can be used to program an external power supply. One advantage of the SMU concept is that a four-terminal device can be completely characterized by the 4145A without changing connections. For example, a bipolar transistor can be characterized in common-base, common-collector and common-emitter configurations without any connection changes.
A.4
Appendix A: Overview of the HP4145A Parameter Analyzer The two additional voltage sources (VS) and two voltage monitors (VM) are built in for measurements that require more sources and/or monitors than are provided by the four SMUs. Each VS is a programmable voltage source [with] ± 1 mV to ± 20 V output. Each VM can measure voltages from ± 100 µV to ± 2 V, or from ± 1 mV to ± 20 V, depending on its range setting. A.6 Instrument Operation The operating system of the 4145A is designed to perform a wide range of operations with menu-driven, softkey-oriented control. The measurement procedures are divided functionally into four parts that are each displayed in a menu page format: CHANNEL DEFINITION, SOURCE SET UP, MEAS & DISP MODE SET UP and DISPLAY (see Figure A.4). These pages can be accessed sequentially by pressing the PREV or NEXT keys and directly from the menu page by pressing the appropriate softkey. The user sets up, or programs, the measurement by filling in blanks on each menu page. The field pointer (►) and system messages displayed on the CRT guide the operator though the programming procedure. If only minor modifications are desired, the field pointer can be moved directly to the target field by pressing the appropriate cursor control keys.
[hp] CHAN SMU1 SMU2 SMU3 SMU4 V1 V2 Vm 1 Vm 2 USER FCTN 1 2 *** CHANNEL DEFINITION *** NAME SOURCE V I MODE FCTN VE IE V VAR1 VB IB COM CONST VCE IC COM CONST –––– –––– –––– –––– V V –––– ––––
–––– ––––
HFE
( (
NAME(UNIT)=EXPRESSION ) = IC/IB )=
Figure A.4a Typical measurement setup procedure for the 4145A. (a) CHANNEL DEFINITION page. The names and source modes for the SMU’s are selected and the names of the voltage sources and monitors are specified. If required, the user functions are defined. A.7 User Functions The 4145A has two programmable user functions which provide real-time calculation of currentvoltage dependent parameters, such as hFE, gm and maximum-power hyperbola. All of the 4145A’s arithmetic functions, variables and physical constants can be used in the equation defining a user function. User functions are executed during measurements and the calculation results can be displayed in the same manner as the measurement results.
A.5
Appendix A: Overview of the HP4145A Parameter Analyzer
[hp]
******
NAME SWEEP MODE START STOP STEP NO. OF STEP COMPLIANCE CONSTANT VB VCE COM COM
SOURCE SET UP VAR1 VE LINEAR .0000V - .9000V - .0100V 91 100.0mA SOURCE .0000V .0000V
****** VAR2 LINEAR ––––––
COMPLIANCE 105.0mA 105.0mA ––––––– –––––––
Figure A.4b: SOURCE SET UP page. The range of values and sweep modes are specified for each source. Delay and hold times can be specified by pressing the proper softkeys.
[hp] ** MEAS & DISP MODE SET UP SWEEP **
MEASUREMENT MODE:
NAME SCL MIN MAX
DISPLAY MODE: X axis VE LINEAR .0000V -1.0000V
GRAPHICS Y1 axis Y2 axis IC IB LOG LOG 1.000pA 1.000pA 100.0mA 100.0mA
Figure A.4c: MEAS & DISP MODE SET UP page. The desired measurement and display modes are selected and the appropriate display variables are designated. A.8 Systems Use The 4145A’s PLOT function dumps all information displayed on the CRT directly onto a digital printer/plotter providing publication-quality hard copies. The PRINT function operates similarly, but only data stored in the measurement data buffer is printed.
A.6