electrical measurement techniques for nanotechnology

8/11/2019 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

[email protected]: 1.613.283.3000; Fax: 1.613.283.6082
mailto:[email protected]:[email protected]


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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


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


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

electrical measurement techniques for nanotechnology

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