Electrical Measurement Techniques for Nanotechnology
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Guildline Instruments Limited2007
Electrical Measurement
Techniques
for Nanometrology
Speaker/Author: Richard Timmons, P.Eng.President, Guildline Instruments
richard.timmons@guildline.comTel: 1.613.283.3000; Fax: 1.613.283.6082
mailto:richard.timmons@guildline.commailto:richard.timmons@guildline.com8/11/2019 Electrical Measurement Techniques for Nanotechnology
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Presentation Overview
DC Electrical Measurements
Nanoscale Range
Low And High Resistances
Low Currents
Low Voltages
Theoretical Frameworks
Techniques And Tips To ImproveAccuracy
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Electrical Standards - Resistance
All Electrical Standards Traceable To National Metrology Institutes
Via17025 Accredited Calibrations
DC Resistance Standards 1 (10-6) to 10 P (10-16)
Uncertainties Range from 0.2 to 5000 ppm
Research Into 0.1 and Smaller Values
Temperature Stabilized Standards
Better Than Traditional Oil Based StandardsBest Uncertainties 0.2 ppm, Annual Drift < 1.5 ppm
Temperature Coefficient < 0.005 ppm
Intrinsic Standard Is Quantum Hall at 12906.4035
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Electrical Standards - Current
Current
Current Shunts 1 Amp to 3000 Amps
Best Uncertainties 1 ppm to 500 ppm
Stable, Linear Performance With Respect to Power
Primary Standard
Current Balance Between 2 Coils of Known Mass
and Dimensions With Uncertainty of 15 ppmPractical Realization of Ampere
From 1A = 1V / 1 With Better Than .001 ppm
Uncertainties
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Electrical Standards - Voltage
Voltage
Typically 1 V to 10 V
Best Uncertainties < 1.0 ppm
Intrinsic Standard Is Josephine Junction Array
Typical Output In mV to 1V Range With Best
Uncertainties In the 0.01 to 0.001 ppm Range
Current Research on Stacked Josephine JunctionArrays to Get Higher Voltages
Precision Voltage Dividers Used to Transfer To
Range of Nanovolts to Kilovolts
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Resistance Measurements
Source Current / Measure Voltage
Source Voltage / Measure Current
Low Resistance MeasurementsHigh Resistance Measurements
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Source Current / Measure Voltage
Best for Low Resistance Measurements (< 1k) Voltage Sources Noisier Than Current Sources For Low
Impedance
The Johnson Voltage Noise At Room Temperature
(270K)
Simplifies to:
k = Boltzmanns Constant, T = Absolute Temperature of Source (K)B = Noise Bandwidth (Hz), and R = Resistance of the Source ()
As DUT Resistance (R) Decreases Noise VoltageDecreases
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Source Voltage / Measure Current
Best for High Resistance Measurements > 10 k
Voltage Sources More Stable When Driving HighImpedance
The Johnson Current Noise At RoomTemperature (270K)
B = Noise Bandwidth (Hz), and R = Resistance of Source ()
As DUT Resistance (R) Increases NoiseCurrent Decreases
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Comparative Results Sourcing Current
Versus Sourcing Voltage
Summary of 50
Measurements
Made at Three
Resistance ValuesUsing a Guildline
DCC Bridge
Sourcing BothCurrent and
Voltage
Test () Source
Current
Uncertainty
(ppm)
Source
Voltage
Uncertainty
(ppm)
1k-1k 0.005 0.206
10k-10k 0.011 0.003
100k-100k 0.217 0.003
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LOW RESISTANCE MEASUREMENT
1k 1k
Source Voltage Source Current
3V, 0.206 ppm Std. Dev. 3.16mA, 0.005 ppm Std. Dev.
At 1kand Lower, Sourcing Current GivesMuch Better Measurements
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MEDIUM RESISTANCE MEASUREMENT
10k 10k
Source Voltage Source Current
10V, 0.003 ppm Std. Dev. 1mA, 0.011ppm Std. Dev.
The 10 k Resistance Level Is the ApproximateTransition Point At Which Both Voltage and CurrentMethods Perform Equally Well With Respect toMeasurement Noise
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HIGH RESISTANCE MEASUREMENT
100k 100k
Source Voltage Source Current
32V, 0.003 ppm Std. Dev. 0.32mA, 0.217 ppm Std. Dev.
At 100 kand Higher Sourcing Voltage Gives
Much Better Measurements
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Very Low Resistance Measurements
100 ResistanceStandard (Guildline9334A)
Below 1 mRecommended toUse Current RangeExtenders
Up to 3000AUncertainties of 10-8ppm or Better
Serial # 50A 75A 100A
68343 99.9871 99.9871 99.9888
69181 99.9803 99.9810 99.9826
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Very Low Resistance Measurements
(cont)
May Need Low Currents Saturation Current For Nanoscale Materials Often
Very Low
Self Heating Effects Create Measurement Errors and
Excessive Heat Can Damage DUT Exception Is Super-Conducting Materials
Current Comparator (CCC) Bridges Can MeasureDown to 10-9 With Low Currents
Thermal Stability Very Important For Both Resistance Standard and DUT
Stable Air Baths (0.001 C)
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Very High Resistance Measurements
DCC bridges measure up to 1 G Provide Better Uncertainties At and Below
100 M
Best Uncertainties of 0.02 to 0.04 ppm For Multi-Ratio Bridges
Teraohmmeters (i.e. electrometer based)Better Above 1G
Measure From 1 M up to 10 P (1016) WithDirect Measurement Uncertainty RangingFrom 0.015% to 5% Across This Range
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Very High Resistance Measurements
(cont)
Teraohmmeter WithMulti-Ratio DirectTransfer ProvidesBest Uncertainties [1]
Transfers (25) To Known1G, 10G and 100GStandards UsingKnown 100MStandard (Ratios Up
to 1:1000)Current Research to1017 Using 1014Standard.
Resistor
Nominal
Value
()
Charted
Uncertainty
(ppm)
Direct
Reading
(ppm)
Transfer
Uncertainty
(ppm)
100M 18 150 30.91G 41 200 33.7
10G 106 600 32.7
100G 94 800 46.6
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Low Current Measurements
Generate or Measure Accurate and
Traceable Low Value Currents
Use Commercial Voltage Standard and
Accurate High Value Resistance Standards Traceable Reference Currents Down to 50 fA
(10-15A)
Can be Verified Using a Teraohmeter [2]
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Low Current Measurements(cont)
Guildline 6520
Teraohmmeter
With Guildline
9336/9337Resistance
Standards [2]
Uncertainties Can Be
Improved by theSubstitution
Method [1]
Resistor9336/9337
TeraohmmeterTest Voltage
EffectiveCurrent Uncertainty
100k 1 V 10 A 0.025 %
1M 1 V 1 A 0.025 %
10M 10 V 1 A 0.025 %
100M 10 V 100 nA 0.015 %
1G 10 V 10 nA 0.02 %
10G 10 V 1 nA 0.06 %
100G 10 V 100 pA 0.08 %
1T 10 V 10 pA 0.1 %10T 10 V 1 pA 0.2 %
100T 10 V 100 fA 0.3 %
1P 10 V 10 fA 1 %
10P 10 V 1 fA 5 %
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Low Voltage Measurements
In Order to Prevent Damage
Unless Material Is Super-Conducting
Nanovolt Meters Can Measure in the
Picovolt (10-12)Range
Johnson Noise (i.e. Motion of Charged
Particles Due to Thermal Energy) Limits
Accuracy of Low Voltage Measurements
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MEASUREMENT TECHNIQUES
AND TIPSTemperature Effects
Digital Filtering
DC Reversal Techniques
Humidity EffectsElectromagnetic Interference (EMI)
Connectors and Leads
Guarding
GroundingSettling Times
Direct Measurement With No Amplification
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Temperature Effects
1.0 Resistance
Standard (Guildline
9334A)
t/c of 8.5 ppm/C
(8.5-12 or 8.5 p)Best Thermometry
Bridges < 0.025 ppm
Ruthenium Oxide Probe
(RTD) For < 1 Kneeds 75 k
Stable Air Baths At
< 1 mK
Serial # 21C
23C
25C
68559 1.000048 1.000065 1.000083
68560 0.999997 1.000015 1.000032
68561 1.00033 1.00034 1.00035
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Digital Filtering
Order of Magnitude of Additional Accuracy
Large Number of Tests Reduces the Bandwidth of the Noise
Ex: Remove Outlier Measurements > k3( i.e. > 3 x standard deviation)
Dynamically Alter the Sampling Times Increase If Measurement Stable
If Periodic, Synchronize To a Clock Telecommunications Industry
Analyze Total Set of Test Results Post Experiment Analysis With PC
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Digital Filtering
(cont)Sophisticated
Techniques IncludeProfiling Noise,Excitation Effects,
Systematic Errors,and Other EffectsWith a SuitableMathematical Model
Use Weighted
CoefficientsEx: Closure Error For aMulti-Ratio GuildlineDCC bridge [3]
Correction
MethodRelative
Improvement
(ppm)
Uncorrected
(BaselineMeasurement)
0.000
Rounding 0.050
LinearInterpolation 0.061
Logarithmic
Weighting
0.084
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DC Reversal Techniques
Polarity Reversal
Eliminate Thermal EMFs
Reduces the Effect of White Noise
Increases the Signal-To-Noise Ratio
Can Be Optimized
Faster When Measured Parameter Is
Changing
Slower When Measured Parameter Is Stable
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Humidity Effects
Make Measurements In a Controlled, Low
Humidity Environment
Essential If DUT Absorbs Water
Use High Quality Insulators
Teflon, Polyethylene, Sapphire
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Electromagnetic Interference
(EMI)EMI Noise In Most Laboratories Florescent Lights, Cell Phones, Fixed Point Temperature
Furnaces, Electric Motors, AC Electrical Power Lines
Ambient EMI Noise Often Higher Than Nanoscale
Electrical MeasurementsInstruments Have Built-in EMI Noise Display Screens, Microprocessors / Microcontrollers, Power
Supplies
EMI Shielding For Both Measurement Circuitry and DUT High Quality Air Baths Provide Both EMI Shielding and
Temperature Stability
Power Line Filters
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Connectors and Leads
4 Terminal Mode Most Accurate Method for Measuring Small Resistances
Corrects For Lead Resistance
Allows Longer Test Leads
Current Supply Compliance ImportantVery Low Resistances May Have Greater Voltage Drop
Across Leads and Connectors Then Across Shunt
Condition of Connectors, Cleanliness Important Poor Measurements From Cracked Terminals, Dirty Contacts,
Moisture Absorbed By Standards and DUTs
Errors As High As 10 ppm
High Resistance Needs Very Good Insulation
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Guarding
Conductor Connected To Low Impedance Point
In Circuit That Is At Nearly Same Potential As
High Impedance Lead Being Guarded
Reduces Leakage Currents and Noise In Test /Measurement Circuits
Very Important For High Resistance Measurements
Measurement Instruments Should Provide Guarded
Connection Terminal
Reduces Effect Of Shunt Capacitance
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Grounding
Single Point Ground For All Components In Test SetupIncluding DUT Avoids Ground Loop Currents Between Measurement Circuit
and DUT, or Measurement Circuit and Test Fixture
Noisy Power Lines Largest Contributor Is Typically PCs
NOT Good Measurement Practice To Connect DifferentComponents Of Test Setup To Different Power Outlets Power Line Grounds May Not Be At Same Electrical Potential,
Thus Creating Spurious CurrentsNOT Good To Connect Instruments Common GroundTo Chassis Ground (i.e. Power Line Ground)
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Settling Times
Needed To Overcome Capacitance
Effects, Self-Heating Effects, Dielectric
Absorption
Present In Measurement Instruments,
Standards, Cabling, DUT
Longer Settling Times Very Important For
Resistances > 100 k
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Direct Measurement With No
AmplificationNOT Recommended To Use Operational
Amplifiers or Other Techniques ToIncrease the Measured Signal
Will Proportionally Increase Noise Operational Amplifiers Or Other Circuitry Will
Introduce Additional Noise
Need Instruments Capable Of DirectlyMeasuring Electrical Properties At VeryLow Values
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References
[1] Mark Evans and Nick Allen, Guildline InstrumentsLimited, Evaluation of a Concept for High OhmsTransfers at Ratios > 10:1, 2007 ConferenceProceedings of the NCSL International Annual
Workshop and Symposium.[2] Mark Evans, Application of the Guildline Model6520 Teraohmmeter for the Nuclear Power Industry,White Paper, Guildline Instruments Limited.
[3] Mark Evans and Xiangxiao Qiu, P. Eng., Guildline
Instruments Limited, Application of Software EnhancedDCC Bridge Measurement, 2005 ConferenceProceedings of the NCSL International AnnualWorkshop and Symposium.
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Providing Precision
Measurement SolutionsGuildline Instruments Limited
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