Keithley - Low Level Measurements Handbook - 7th Edition Precision DC Current, Voltage and Resistance Measurements.pdf

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Low Level Measurements
Handbook - 7
th
Edition
Precision DC Current, Voltage,
and Resistance Measurements
Low Level
Measurements
Handbook
Precision DC Current, Voltage,
and Resistance Measurements
SEVENTH EDITION
C
ontents
SECTION 1
Low Level DC Measuring Instruments
1.1
1.2
1.3
Introduction ...............................................................................................
1-3
Theoretical Measurement Limits ..........................................................
1-3
Instrument Definitions ............................................................................
1-5
1.3.1
1.3.2
1.3.3
1.3.4
1.3.5
1.3.6
1.3.7
1.3.8
1.4
The Electrometer ......................................................... 1-5
The DMM ......................................................................1-7
The Nanovoltmeter .......................................................1-7
The Picoammeter ......................................................... 1-8
The Source Measure Unit Instrument ......................... 1-8
The Low Current Preamp ............................................ 1-9
The Micro-ohmmeter ................................................... 1-9
The Low Current Source ............................................. 1-9
Definition of Accuracy Terms .....................................1-10
Accuracy ......................................................................1-11
Deratings .....................................................................1-15
Noise and Noise Rejection ..........................................1-15
Speed ..........................................................................1-17
Voltmeter Circuits .......................................................1-17
Ammeter Circuits ........................................................1-19
Coulombmeter Circuit ................................................1-23
High Resistance Ohmmeter Circuits ..........................1-24
Low Resistance Ohmmeter Circuits............................1-26
Complete Instruments ............................................... 1-28
Understanding Instrument Specifications .......................................
1-10
1.4.1
1.4.2
1.4.3
1.4.4
1.4.5
1.5
Circuit Design Basics .............................................................................
1-17
1.5.1
1.5.2
1.5.3
1.5.4
1.5.5
1.5.6
SECTION 2
Measurements from High Resistance Sources
2.1
2.2
Introduction ...............................................................................................
2-2
Voltage Measurements from High Resistance Sources ...................
2-2
2.2.1 Loading Errors and Guarding...................................... 2-3
2.2.2 Insulation Resistance of the Test Circuit ....................2-11
2.3
Low Current Measurements ................................................................
2-15
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
Leakage Currents and Guarding ................................2-15
Noise and Source Impedance .....................................2-21
Zero Drift ................................................................... 2-23
Generated Currents ................................................... 2-23
Voltage Burden ...........................................................2-31
Low Level Measurements Handbook
iii
2.3.6 Overload Protection ................................................... 2-33
2.3.7 AC Interference and Damping ................................... 2-34
2.3.8 Using a Coulombmeter to Measure Low Current ..... 2-35
2.4
High Resistance Measurements .........................................................
2-39
2.4.1 Constant-Voltage Method........................................... 2-40
2.4.2 Constant-Current Method ......................................... 2-41
2.5
Charge Measurements..........................................................................
2-46
2.5.1
2.5.2
2.5.3
2.6
Error Sources ............................................................. 2-47
Zero Check ................................................................. 2-48
Extending the Charge Measurement Range
of the Electrometer .................................................... 2-48
Making Connections .................................................. 2-50
Electrostatic Interference and Shielding ....................2-51
Environmental Factors............................................... 2-55
Speed Considerations ................................................ 2-56
Johnson Noise ............................................................ 2-62
Device Connections ................................................... 2-66
Analog Outputs .......................................................... 2-69
Floating Input Signals .................................................2-70
General Electrometer Considerations...............................................
2-49
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
2.6.6
2.6.7
2.6.8
2.7
High Impedance Measurement Optimization Summary..............
2-71
SECTION 3
Measurements from Low Resistance Sources
3.1
3.2
Introduction ...............................................................................................
3-2
Low Voltage Measurements ...................................................................
3-2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.2.9
3.2.10
3.2.11
3.2.12
Effects of Error Sources on Voltage Measurements .... 3-2
Thermoelectric EMFs ................................................... 3-3
Internal Offsets ............................................................ 3-7
Zero Drift ..................................................................... 3-7
RFI/EMI ........................................................................ 3-9
Johnson Noise .............................................................3-10
1/f Noise ......................................................................3-11
Line Cycle Interference and Line Cycle Integration .. 3-12
Magnetic Fields .......................................................... 3-13
Ground Loops .............................................................3-14
Ways to Reduce Noise .................................................3-16
Common-Mode Current and Reversal Errors ............3-17
iv
3.3
Low Resistance Measurements..........................................................
3-18
3.3.1 Lead Resistance and Four-Wire Method .................... 3-18
3.3.2 Thermoelectric EMFs and
Offset Compensation Methods .................................. 3-20
3.3.3 Non-Ohmic Contacts ................................................. 3-25
3.3.4 Device Heating ........................................................... 3-26
3.3.5 Dry Circuit Testing ..................................................... 3-27
3.3.6 Testing Inductive Devices .......................................... 3-28
3.4
Measurement Optimization Summary for
Low Impedance Measurements .........................................................
3-29
SECTION 4
Applications
4.1
4.2
Introduction ..............................................................................................
4-2
Applications for Measuring Voltage from
High Resistance Sources ........................................................................
4-2
4.2.1 Capacitor Dielectric Absorption ................................. 4-2
4.2.2 Electrochemical Measurements .................................. 4-6
4.3
Low Current Measurement Applications ...........................................
4-9
Capacitor Leakage Measurements .............................. 4-9
Low Current Diode Measurements .......................... 4-13
Low Current Measurements of MOSFETs...................4-16
Light Measurements with Photomultiplier Tubes ..... 4-18
Ion Beam Measurements .......................................... 4-21
Photoconductive Current of PIN Photodiode ........... 4-23
Avalanche Photodiode Reverse Bias Current
Measurements ............................................................ 4-24
4.3.8 Current-Voltage Characterization of
Carbon Nanotube (CNT) FETs .................................. 4-26
4.4
High Resistance Measurement Applications ..................................
4-28
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.3.7
4.4.1
Surface Insulation Resistance Testing of
Printed Circuit Boards .............................................. 4-28
4.4.2 Resistivity Measurements of Insulating Materials .... 4-30
4.4.3 Resistivity Measurements of Semiconductors .......... 4-34
4.4.4 Voltage Coefficient Testing of High Ohmic
Value Resistors .......................................................... 4-44
4.5
Charge Measurement Applications ..................................................
4-45
4.5.1
Capacitance Measurements ...................................... 4-45
Low Level Measurements Handbook
v

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