TECHNIQUES FOR MEASURING RESISTIVITY FOR MATERIALS .
TECHNIQUES FOR MEASURINGRESISTIVITY FOR MATERIALSCHARACTERIZATION––4200A-SCS PARAMATER ANALYZER APPLICATIONS GUIDE
TECHNIQUES FOR MEASURING RESISTIVITY FORMATERIALS CHARACTERIZATION APPLICATIONS GUIDEWhich Kelvin method is right for your resistivity measurements? The two application notes in this materialscharacterization applications guide offer tips and techniques for choosing between the Four-Point CollinearProbe or van Der Pauw methods based on the type, shape, and thickness of your material and themagnitude of its resistance.CONTENTSResistivity Measurements of Semiconductor MaterialsUsing the 4200A-SCS Parameter Analyzer and aFour-Point Collinear Probe. 3van der Pauw and Hall Voltage Measurements withthe4200A-SCS Parameter Analyzer. 8WWW.TEK.COM 1
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Resistivity Measurements of SemiconductorMaterials Using the 4200A-SCS Parameter Analyzerand a Four-Point Collinear ProbeIntroductionElectrical resistivity is a basic material property that quantifiesThe Four-Point CollinearProbe Methoda material’s opposition to current flow; it is the reciprocalThe most common way of measuring the resistivity of aof conductivity. The resistivity of a material depends uponseveral factors, including the material doping, processing,and environmental factors such as temperature and humidity.The resistivity of the material can affect the characteristicsof a device of which it’s made, such as the series resistance,threshold voltage, capacitance, and other parameters.semiconductor material is by using a four-point collinearprobe. This technique involves bringing four equally spacedprobes in contact with a material of unknown resistance. Theprobe array is placed in the center of the material, as shownin Figure 1.HIDetermining the resistivity of a material is common in bothLOSource currentfrom 1 to 4research and fabrication environments. There are manymethods for determining the resistivity of a material, but theHItechnique may vary depending upon the type of material,VMeasure voltagebetween 2 and 3LOmagnitude of the resistance, shape, and thickness of thematerial. One of the most common ways of measuring4-PointCollinear Probethe resistivity of some thin, flat materials, such assemiconductors or conductive coatings, uses a four-point1collinear probe. The four-point probe technique involvesbringing four equally spaced probes in contact with a material234Semiconductor Waferof unknown resistance. A DC current is forced between theouter two probes, and a voltmeter measures the voltagedifference between the inner two probes. The resistivity iscalculated from geometric factors, the source current, andthe voltage measurement. The instrumentation used for thistest includes a DC current source, a sensitive voltmeter, and afour-point collinear probe.To simplify measurements, the 4200A-SCS ParameterFigure 1. Four-point probe resistivity test circuitThe two outer probes are used for sourcing current and thetwo inner probes are used for measuring the resulting voltagedrop across the surface of the sample. The volume resistivityis calculated as follows:Analyzer comes with a project that contains tests for makingresistivity measurements using a four-point collinear probe.The 4200A-SCS can be used for a wide range of materialresistances including very high resistance semiconductormaterials because of its high input impedance ( 1016 ohms).This application note explains how to use the 4200A-SCSwith a four-point collinear probe to make resistivitymeasurements on semiconductor materials.ρ where: ρπ V t kln 2 I volume resistivity (Ω-cm)V the measured voltage (volts)I the source current (amperes)t the sample thickness (cm)k* a correction factor based on the ratio of theprobe to wafer diameter and on the ratio ofwafer thickness to probe separation* The correction factors can be found in standard four-point proberesistivity test procedures such as SEMI MF84-02—Test Methodfor Measuring Resistivity of Silicon Wafers with an In-Line FourPoint Probe.WWW.TEK.COM 3
Resistivity Measurements of Semiconductor Materials Using the4200A-SCS Parameter Analyzer and a Four-Point Collinear ProbeAPPLICATIONS GUIDEFor some materials such as thin films and coatings, theNotice that the current flows through all the resistances in thesheet resistance, or surface resistivity, is determined instead,first and fourth set of leads and probes, as well as throughwhich does not take the thickness into account. The sheetthe semiconductor material. However, the voltage is onlyresistance (σ) is calculated as follows:measured between probes 2 and 3. Given that betweenπ V Vσ k 4.532 kln2 IIvoltage drop due to RS2 will be measured by the voltmeter. Allwhere: σ the sheet resistance (Ω/square or just Ω)not be measured.probes 2 and 3, the current only flows through RS2, only theNote that the units for sheet resistance are expressed interms of Ω/square in order to distinguish this number from themeasured resistance (V/I).Using the Kelvin Technique to Eliminate Lead andContact Resistancethe other unwanted lead (RL) and contact (RC) resistances willUsing the 4200A-SCSto Make Four-Point ProbeCollinear Probe MeasurementsThe 4200A-SCS comes with a project that is alreadyUsing four probes eliminates measurement errors due toconfigured for automating four-point probe resistivitythe probe resistance, the spreading resistance under eachmeasurements. The project, Four-Point Probe Resistivityprobe, and the contact resistance between each metalProject, can be found in the Project Library in the Selectprobe and the semiconductor material. Figure 2 is anotherview by selecting the Materials filter. This project has tworepresentation of the four-point collinear probe setup thattests: one measures the resistivity using a single test currentshows some of the circuit resistances.and the other measures the resistivity as a function of acurrent sweep. These two tests, Four-Point Probe ResistivitySource CurrentHIHIR L1R L2Measurement (4-pt-collinear) and Four-Point ProbeLOResistivity Sweep (4-pt-resistivity-sweep), can also be foundLOVR L3R L4R L Lead ResistanceR C Contact ResistanceR S Sample ResistanceV Measured Voltage BetweenProbes 2 And 3Only the voltage drop due to RS2 ismeasured by the voltmeter.1RCRC1232R S1VR S2RC34RC4R S3Figure 2. Test setup showing circuit resistancesThe RL terms represent the test lead resistance. RCin the Test Library and can be added to a project. A screencapture of the Four-Point Probe Resistivity Measurement testis shown in Figure 3.The projects and tests included with the 4200A-SCS areconfigured to use either three or four SMUs (Source MeasureUnits). When using three SMUs, all three SMUs are setto Current Bias (voltmeter mode). However, one SMU willsource current (pin 1 of probe) and the other two (pins 2 and3 of probe) will be used to measure the voltage differencebetween the two inner probes. An example of how this isset up with the 4200A-SCS is shown in Figure 4. One SMUrepresents the contact resistance between the metal probe(SMU1) and the GNDU (ground unit) are used to sourceand the semiconductor material. The contact resistancecurrent between the outer two probes. The other SMUscan be several hundred to a thousand times higher than the(SMU2 and SMU3) are used to measure the voltage dropresistance of the sample material, which is represented by RS.between the two inner probes.When configuring the tests, enter an appropriate test currentfor SMU1. This will depend on the resistivity of the sample.For higher resistance samples, additional Interval time mayneed to be added in the Test Settings pane to ensure asettled reading.4 WWW.TEK.COM
Resistivity Measurements of Semiconductor Materials Using the4200A-SCS Parameter Analyzer and a Four-Point Collinear ProbeAPPLICATIONS GUIDEFigure 3. Screen Capture of Four-Point Probe Resistivity Measurement Test in the Clarius softwareUsing the Formulator,calculate the voltagedifference betweenSMU2 and SMU3.SMU1: Set toCurrent Bias (VMU)– Set current levelto have about a10mV drop betweenSMU2 and SMU3.SMU2: Set toCurrent Bias (VMU)– Use as high impedance voltmeter,and set current to0A on 1nA range.SMU3: Set toCurrent Bias (VMU)– Use as high impedance voltmeter,and set current to0A on 1nA range.GNDU: Commonconnection for allSMUs. Or, this canbe SMU4 set toCommon.Force HIForce HIForce HIForce HIFigure 4. SMU Instrument Designation for Four-Point Collinear Probe MeasurementWWW.TEK.COM 5
Resistivity Measurements of Semiconductor Materials Using the4200A-SCS Parameter Analyzer and a Four-Point Collinear ProbeAPPLICATIONS GUIDEFigure 5. Formulator dialog box with resistivity calculations in the Four Point Probe Resistivity Project.The voltage difference between SMU2 and SMU3 isSources of Error andMeasurement Considerationscalculated: VDIFF SMU2V-SMU3V. The sheet resistivityFor successful resistivity measurements, potential(ohms/square) is derived from SMU1 current and voltagesources of errors need to be considered.The Formulator in the Test Settings pane includesequations to derive the resistivity as shown in Figure 5.difference calculation, SHEET RHO 4.532*(VDIFF/SMU1I).To determine the volume resistivity (ohms-cm), multiply theElectrostatic Interferencesheet resistivity by the thickness of the sample in centimetersElectrostatic interference occurs when an electrically(cm). If necessary, a correction factor can also be applied tocharged object is brought near an uncharged object. Usually,the formula.the effects of the interference are not noticeable becauseAfter the test is configured, lower the probe head so the pinsare in contact with the sample. Execute the test by selectingRun at the top of the screen. The resistivity measurementswill appear in the Sheet in the Analyze view.the charge dissipates rapidly at low resistance levels.However, high resistance materials do not allow the chargeto decay quickly and unstable measurements may result.The erroneous readings may be due to either DC or ACelectrostatic fields.To minimize the effects of these fields, an electrostaticshield can be built to enclose the sensitive circuitry. Theshield is made from a conductive material and is alwaysconnected to the low impedance (FORCE LO) terminal of theSMU instrument.The cabling in the circuit must also be shielded. Low noiseshielded triax cables are supplied with the 4200A-SCS.6 WWW.TEK.COM
Resistivity Measurements of Semiconductor Materials Using the4200A-SCS Parameter Analyzer and a Four-Point Collinear ProbeAPPLICATIONS GUIDELeakage CurrentCarrier InjectionFor high resistance samples, leakage current may degradeTo prevent minority/majority carrier injection from influencingmeasurements. The leakage current is due to the insulationresistivity measurements, the voltage difference betweenresistance of the cables, probes, and test fixturing. Leakagethe two voltage sensing terminals should be kept at lesscurrent may be minimized by using good quality insulators, bythan 100mV, ideally 25mV, since the thermal voltage, kt/q, isreducing humidity, and by using guarding.approximately 26mV. The test current should be kept as lowA guard is a conductor connected to a low impedance pointin the circuit that is nearly at the same potential as the highas possible without affecting the measurement precision.impedance lead being guarded. The inner shield of the triaxConclusionconnector of the 4200A-SCS is the guard terminal. This guardThe 4200A-SCS Parameter Analyzer is an ideal tool forshould be run from the 4200A-SCS to as close as possible tomeasuring resistivity of semiconductor materials using a four-the sample. Using triax cabling and fixturing will ensure thatpoint collinear probe. The built-in resistivity project and teststhe high impedance terminal of the sample is guarded. Theare configurable and include the necessary calculations.guard connection will also reduce measurement time sincethe cable capacitance will no longer affect the time constantof the measurement.LightCurrents generated by photoconductive effects can degradeBibliographyASTM, F76-86. Standard Method for Measuring Hall Mobilityand Hall Coefficient in Extrinsic Semiconductor SingleCrystals. Annual Bk. ASTM Stds., 1999: 10.05.measurements, especially on high resistance samples. ToSEMI MF84-02: Test Method for Measuring Resistivityprevent this, the sample should be placed in a dark chamber.of Silicon Wafers With an In-Line Four-Point Probe. LastTemperatureThermoelectric voltages may also affect measurementaccuracy. Temperature gradients may result if the sampletemperature is not uniform. Thermoelectric voltages mayalso be generated from sample heating caused by thesource current. Heating from the source current will morelikely affect low resistance samples, because a higher testpublished by ASTM International as ASTM F 84-02.van der Pauw, L. J. A Method of Measuring SpecificResistivity and Hall Effects of Discs of Arbitrary Shape. PhipsRec. Repts., 1958: 13 1.Schroder, Dieter K. Semiconductor Material and DeviceCharacterization. John Wiley & Sons, Inc., 1998.current is needed to make the voltage measurements easier.Low Level Measurements, Keithley Instruments, Inc.,Temperature fluctuations in the laboratory environmentCleveland, Ohio, 2014.may also affect measurements. Because semiconductorshave a relatively large temperature coefficient, temperaturevariations in the laboratory may need to be compensated forby using correction factors.WWW.TEK.COM 7
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerIntroductionSemiconductor material research and device testing oftenvan der Pauw ResistivityMeasurement Methodinvolve determining the resistivity and Hall mobility of aThe van der Pauw method involves applying a currentsample. The resistivity of semiconductor material is primarilydependent on the bulk doping. In a device, the resistivitycan affect the capacitance, the series resistance, and the threshold voltage.and meas uring voltage using four small contacts on thecircumference of a flat, arbitrarily shaped sample of uniformthickness. This method is particularly useful for measuringvery small samples because geometric spacing of theThe resistivity of the semiconductor material is oftencontacts is unimportant. Effects due to a sample’s size,determined using a four-point probe technique. With a four-which is the approximate probe spacing, are irrelevant.probe, or Kelvin, technique, two of the probes are used toUsing this method, the resistivity can be derived from a totalsource current and the other two probes are used to measurevoltage. Using four probes eliminates measurement errorsdue to the probe resistance, the spreading resistance undereach probe, and the contact resist ance between each metalof eight measurements that are made around the peripheryof the sample with the configurations shown in Figure 1.Once all the voltage measurements are taken, two valuesprobe and the semiconductor material. Because a highof resistivity, ρA and ρB, are derived as follows:impedance voltmeter draws little current, the voltage dropsπ (V1 – V2 V3 – V4)ρA fAtsln 24Iacross the probe resistance, spreading resist ance, andcontact resistance are very small.One common Kelvin technique for determining the resistivityπ (V5 – V6 V7 – V8)ρB fBtsln 24Iof a semiconductor material is the van der Pauw (VDP)where: ρA and ρB are volume resistivities in ohm-cm;method. The 4200A-SCS Parameter Analyzer includes ats is the sample thickness in cm;project for making van der Pauw measurements. Because ofits high input impedance ( 1016Ω) and accurate low currentsourcing, the 4200A-SCS with preamps is ideal for highV1–V8 represents the voltages measured by the voltmeter;I is the current through the sample in amperes;resistance samples. This application note explains how tofA and fB are geometrical factors based on sample symmetry.make resist ivity measurements of semiconductor materialsThey are related to the two resistance ratios QA and QB asusing the 4200A-SCS and the van der Pauw method.shown in the following equations (fA fB 1 for perfect symmetry).V51243V3121212434343V7V1V61243V2Figure 1. van der Pauw Resistivity Conventions8 WWW.TEK.COMV4121212434343V8
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerAPPLICATIONS GUIDEQA and QB are calculated using the measured voltagesThe 4200A-SCS with four SMU instruments and four preampsas follows:(for high resistance measurements) is an ideal solution forV1 – V2QA V3 – V4meas uring van der Pauw resistivity, and should enablemeasurements of resistances greater than 1012Ω. Since eachSMU instrument can be configured as a current source or asV5 – V6QB V7 – V8a voltmeter, no external switching is required, thus eliminatingleakage and offsets errors caused by mechanical switches.This removes the need for additional instruments andAlso, Q and f are related as follows:Q – 1f arc coshQ 1 0.693(e0.693/f2)programming.For high resistance materials, a current source that canA plot of this function is shown in Figure 2. The value of f canoutput very small current with a high output impedancebe found from this plot once Q has been calculated.is necessary. A differential electrometer with high inputOnce ρA and ρB are known, the average resistivity (ρAVG) canbe determined as follows:sample. On the lowest current source ranges (1pA and 10pA)of the 4200A-SCS, the input resistance of the voltmeterρA ρBρAVG 2is 1016Ω.Using the 4200A-SCS toMeasure Resistivity with thevan der Pauw Method1.00.9Each terminal of the sample is connected to one SMU0.8fimpedance is required to minimize loading effects on theinstrument, so a 4200A-SCS with four SMU instruments isrequired. The van der Pauw Project, which has four tests,0.7is in the Projects Library and can be found by selecting theMaterials box from the Select pane. A screen capture of the0.6van der Pauw project is shown in Figure 3.0.5Each test has a different measurement setup. A diagramof how the four SMU instruments are configured in the0.4110100QFigure 2. Plot of f vs. Qfour tests is shown in Figure 4. For each test, three of theSMU instruments are configured as a current bias and avoltmeter (VMU). One of these SMU instruments applies thetest current and the other two SMU instruments are usedas high impedance voltmeters with a test current of zeroTest Equipmentamps on a low current range (typically 1nA range). The fourthThe electrical measurements for determining van dercalculated between the two SMU instruments set up as highPauw resistivity require a current source and a voltmeter.impedance voltmeters. This measurement setup is duplicatedTo automate measurements, one might typically use aaround the sample, with each of the four SMU instrumentsprogrammable switch to switch the current source and thechanging functions in each of the four tests. The test currentvoltmeter to all sides of the sample. However, the 4200A-SCSand voltage differences between the terminals from theis more efficient than this.four tests are used to calculate the resistivity in the subsiteSMU instrument is set to common. The voltage difference iscalc sheet.WWW.TEK.COM 9
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerFigure 3. van der Pauw ProjectTest Name:i4-v12Test Name:i2-v34CommonCurrent Bias ( )SMU1SMU2CommonCurrent Bias rSMU4SMU3Current Bias ( urrent Bias ( )CommonSMU12SMU4VoltmeterSMU2Current Bias ( )SMU221434SMU3Current Bias (–)VoltmeterSMU11Figure 4. SMU Instrument Configurations for van der Pauw Measurements10 WWW.TEK.COMSMU4SMU3Current Bias (–)CommonTest Name:i1-v23Test VoltmeterV41VoltmeterSMU4CommonCurrent Bias 1243V23SMU3Voltmeter
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerAPPLICATIONS GUIDETest Configurations for Measuringvan der Pauw Resistivityare averaged using the AVG function with an equation, suchIn each of the four tests, one SMU instrument is configuredlocated on the Test Settings pane, the average voltage (V23)as the current source using the current list sweep function,is selected so that it is sent to the subsite data sheet, where ittwo SMU instruments are configured as voltmeters, and onewill be used in the resistivity calculation. The magnitude of theis configured as a common. Here is the configuration for thecurrent source must also be sent to the subsite data sheet, soi1-v23 test:click that check box (I1) as well.Terminal 1 – SMU1: Set to a two-point Current List Sweep.This same procedure is repeated in all four tests so thatEnter both the positive and negative values of the appropriateall sides of the sample are measured, as shown previouslysource current. Enter the Compliance level and use the Bestin Figure 1. The average voltages from each test are thenFixed source range. Averaging voltage measurements (fromused to calculate the resist ivity on the subsite Calc sheet.SMU2 and SMU3) taken at both a positive and negative testA diagram showing how the SMUs are set up in each test iscurrent will correct for voltage offsets in the circuit.shown in Figure 4.Terminal 2 – SMU2: Set to Current Bias (VMU) with a testAdjusting the Source Currentcurrent of 0A. Set the appropriate compliance voltage, andThe source current value will need to be modified accordingcheck the Measure Voltage box (VB). Even though 0A willbe output, select an appropriate current source range. Theinput impedance of the voltmeter is directly related to thecurrent source range. The lower the current source range is,the higher the input impedance will be. However, the lowerthe current source range, the slower the measurement timeas V23 AVG(ABSV23). In the Output Values d ialog boxto the expected sample resistance. Adjust the current so thatthe voltage difference will not exceed 25mV (approximately).In each of the four tests (i2-v34, i3-v41, i4-v12, i1-v23), enterboth polarities of the test current. The same magnitude mustbe used for each test.will be. For most applications, the 1nA range may be used.Determining the Settling TimeHowever, for very high resistance measurements, use a lowerFor high resistance samples, it will be necessary tocurrent range.Terminal 3 – SMU3: Set up the same as Terminal B.Terminal 4 – SMU4: Set the Operation Mode to Common.In this test, the current is sourced between Terminals 1 and4 (SMU1 to SMU4). SMU2 will measure the voltage fromdetermine the settling time of the measurement. This canbe accomplished by sourcing current into two terminals ofthe sample and measuring the voltage difference betweenthe other two terminals. The settling time can be determinedby graphing the voltage difference versus the time of themeasurement.Terminal 2 to Terminal 4. SMU3 will measure the voltage fromUsing the 4200A-SCS, the voltage versus time graph canTerminal 3 to Terminal 4.easily be created by copying and pasting one of the testsThe Formulator calculates the voltage difference betweenSMU2 and SMU3 for both the positive and negative testcurrent. This can be done using an equation such asV23DIFF V2-V3. The absolute values of these numbers(from both the positive and negative test current) aretaken using the ABS function with an equation such asV23ABS ABS(V23DIFF). The two voltage difference valuesdescribed previously. In the Test Settings pane, take a fewhundred or so readings with a sweep time of one second.Make sure that the Timestamp box is selected. After thereadings are done, plot the voltage difference versus timeon the graph. (You can choose the parameters to graph byusing Graph Settings.) The settling time is determined fromthe graph. A timing graph of a very high resistance material isshown in Figure 5.WWW.TEK.COM 11
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerFigure 5. Voltage vs. Time Graph of Very High Resistance SampleFigure 6. Subsite Data “Calc” Sheet with Resistivity Displayed12 WWW.TEK.COM
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerDetermine the settling time by visually inspecting the voltagedifference vs. time graph. Once the settling time has beendetermined, use this time as the Sweep Delay (in the TestSettings pane) for the four resistivity measurement testslisted previously. This settling time procedure will need to berepeated for different materials; however, it is not necessaryfor low resistance materials since they have a shortAPPLICATIONS GUIDEHall Voltage MeasurementsHall effect measurements are important to semiconductormaterial characterization because from the Hall voltage,the conductivity type, carrier density, and mobility can bederived. With an applied magnetic field, the Hall voltage canbe measured using the configurations shown in Figure 7.settling time.Calculating the ResistivityTo view the calculated resistivity in the subsite level, selectthe subsite plan in the Project Tree. The Output ValuesV(voltage differences and test current) will appear on the data1243V1243sheet at the subsite level. The resistivity is calculated on theCalc sheet from the cell references on the Data sheet. Thethickness, coefficients, and correction factors are also inputon the Calc sheet for the resistivity equation.Figure 7. Hall Voltage Measurement ConfigurationsWith a positive magnetic field, B, apply a current betweenThese values can be updated in the Calc sheet in theterminals 1 and 3, and measure the voltage drop (V2–4 )subsite level. Select the subsite “vdp-test.” Go to thebetween terminals 2 and 4. Reverse the current and measureSubsite Data tab. It contains the output values of the voltagethe voltage drop (V4–2 ). Next, apply current between terminalsdifferences and the test current. From the Calc Sheet tab,2 and 4, and measure the voltage drop (V1–3 ) betweenthe thickness can be adjusted. The default thickness is 1cm.terminals 1 and 3. Reverse the current and measure theIf necessary, a correction factor can also be applied to thevoltage (V3–1 ) again.resistivity equation.Reverse the magnetic field, B, and repeat the procedureRunning the Projectagain, measuring the four voltages: (V2–4–), (V4–2–), (V1–3–),The van der Pauw Project (vdp-resistivity) must be run atand (V3–1–).the subsite level. Make sure that all boxes in the Project areFrom the eight Hall voltage measurements, the average Hallchecked and select the vdp-test subsite. Execute the projectby using the Run button. Each time the test is run, the subsitedata is updated. The voltage differences from each of the fourtests (i2-v34, i3-v41, i4-v12, i1-v23) will appear in the SubsiteData “vdp-device” sheet. The resistivity will appear in theSubsite Data “Calc” sheet as shown in Figure 6.coefficient can be calculated as follows:ts (V4–2 – V2–4 V2–4– – V4–2–)RHC 4BIts (V3–1 – V1–3 V1–3– – V3–1–)RHD 4BIwhere: RHC and RHD are Hall coefficients in cm3/C;ts is the sample thickness in cm;V represents the voltages measured by the voltmeter;I is the current through the sample in amperes;B is the magnetic flux in Vs/cm2 (1 Vs/cm2 108 gauss)Once RHC and RHD have been calculated, the average Hallcoefficient (RHAVG) can be determined as follows:WWW.TEK.COM 13
van der Pauw and Hall Voltage Measurementswith the 4200A-SCS Parameter AnalyzerRHC RHDRHAVG 2resistance of the cables, probes, and test fixturing. LeakageFrom the resistivity (ρAVG) and the Hall coefficient (RHAVG), thereducing humidity, and by using guarding.mobility (μH) can be calculated: RH µH ρAVGUsing the 4200A-SCS to Measure the Hall VoltageThe setup to measure the Hall voltage is very similar to thesetup for measuring resistivity. The difference is the locationof the current source and voltmeter terminals. Figure 7illustrates the setup for Hall voltage measurements. (Figure 4illustrates the setup for resistivity measurements.) If the usersupplied electromagnet has an IEEE-488 interface, a programcan be written in KULT (Keithley User Library Tool) to controlthe electromagnet using the 4200A-SCS. This would requirethat the 4200A-SCS have the 4200-COMPILER option.current may be minimized by using good quality insulators, byA guard is a conductor connected to a low impedance pointin the circuit that is nearly at the same potential as the highimpedance lead being guarded. The inner shield of the triaxconnector of the 4200-SMU is the guard terminal. This guardshould be run from the 4200-SMU to as close as possible tothe sample. Using triax cabling and fixturing will ensure thatthe high impedance terminal of the sample is guarded. Theguard connection will also reduce measurement time sincethe cable capacitance will no longer affect the time constantof the measurement.LightCurrents generated by photoconductive effects can degrademeasurements, especially on high resistance samples. ToSources of Error andMeasurement Considerationsprevent this, the sample should be placed in a dark chamber.For successful resistivity measurements, the potentialThermoelectric voltages may also affect measurementsources of errors need to be considered.accuracy. Temperature gradients may result if the sampleTemperaturetemperature is not uniform. Thermoelectric voltages mayElectrostatic Interferencealso be generated from sample heating caused by theElectrostatic interference occurs when an electricallysource current. Heating from the source current will morecharged object is brought near an uncharged object. Usually,likely affect low resistance samples because a higher testthe effects of the interference are not noticeable becausecurrent is needed to make the voltage measurements easier.the charge dissipates rapidly at low res
* The correction factors can be found in standard four-point probe resistivity test procedures such as SEMI MF84-02—Test Method for Measuring Resistivity of Silicon Wafers with an In-Line Four-Point Probe. Resistivity Measurements of Semiconductor Materials Using the 4200
6 Resistivity Profiling for Mapping Gravel Layers, Amargosa Desert Research Site, Nevada resistivity soundings and multielectrode resistivity profiling. Models selected from the resistivity data are presented and interpreted, with particular attention to resistivity sections produced from the multielectrode transect measurements.
the materials show very less resistivity change even at high pressure i.e. 10 GPa. The change can be calculated by subtracting resistivity value at 10 GPa and at atmospheric pressure. This difference can be divided by the original resistivity value (at atmospheric pressure) and multiplied by 100 to get the percentage resistivity change.
Resistivity is also sometimes referred to as "Specific Resistance" because, from the above formula, Resistivity (Ω-m) is the resistance b Soil Resistivity In the USA, a measurement of -cm is used. (100 -cm 1 -m) 1.3 MAKING A MEASUREMEN the soil is required. The procedure and result interpretation. 1.3.1 PRINCIPLES Soil resistivity va
The direct-current resistivity method is used to determine the electrical resistivity structure of the subsurface. Resistivity is defined as a measure of the opposition to the flow of electric current in a material. The resistivity of a soil or rock is dependent on several factors that include amount of
surface resistivity testing. This method helps in determining key mixture parameters such as fly ash content and w/cm of placed concrete. Based on the gain in resistivity over time, it was found that the slope of the surface resistivity versus time curve could be used to differentiate fly ash content. And, the resistivity value
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5.1 Soil resistivity measurements Soil resistivity is very important factor for earthing system designing so more attention required while measuring soil resistivity. The resistivity of soil varies appreciably with depth and also horizontally, it is often desirable to use an increased range of probe spacing on order to obtain an
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