“The study of material properties is an important part of contemporary materials science. The so-called material properties refer to the quantitative measurement and description of the functional properties and utility of materials, that is, the material’s response to electrical, magnetic, optical, thermal, and mechanical loads. The source meter SMU plays a pivotal role in contemporary material science research. Choosing an SMU suitable for electrical performance testing of a certain type of material, how to reduce the test error, and what should be paid attention to in the test, these issues need to be focused on.
Preface: The study of material properties is an important part of contemporary materials science. The so-called material properties refer to the quantitative measurement and description of the functional properties and utility of materials, that is, the material’s response to electrical, magnetic, optical, thermal, and mechanical loads. The source meter SMU plays a pivotal role in contemporary material science research. Choosing an SMU suitable for electrical performance testing of a certain type of material, how to reduce the test error, and what should be paid attention to in the test, these issues need to be focused on. Tektronix Keithley’s brand enjoys a high reputation among engineers and scientists in many disciplines around the world. Its high-precision source meters (SMU), multimeters, precision power supplies, small signal testing and data acquisition products are contemporary with Tektronix’ original product lines. Materials science research provides a variety of test programs.
[Contemporary Materials Electrical Testing Classroom]The series involves the cutting-edge electrical transport and quantum material/superconducting material testing of contemporary materials science, one-dimensional/carbon nanotube material testing, two-dimensional material and graphene testing, and application testing of nanomaterials. Today I will share with you the third chapter,[Contemporary Material Electrical Testing Classroom]Series Three: Physical Property Characterization Test in Condensed Matter Physics.
Condensed matter physics is a science that studies the microstructure of condensed matter composed of a large number of microscopic particles (atoms, molecules, ions, electrons), the interaction between particles, the laws of motion, and the properties and applications of materials. It is the science of contemporary materials science. Fundamentals of physics. The main research directions of condensed matter physics are: the basic Electronic properties of high-temperature superconductors and related strongly correlated systems, low-dimensional spin and charge systems, the basic electronic properties of nano-functional materials, the basic properties of spintronics materials, etc. Materials/superconducting materials/semi-metal materials/heterostructure materials/superhard materials are all subjects of condensed matter physics research.
Comprehensive physical property test is the main test of condensed matter physics, including electrical transport test such as: resistivity, differential resistance, Hall coefficient, volt-ampere characteristics, critical current, etc.; magnetic test such as: AC magnetic susceptibility, hysteresis loop , Magnetoresistance, etc.; thermal tests such as: specific heat, thermomagnetic curve, thermoelectric effect, Seebeck coefficient, thermal conductivity, etc.; also include optical tests, pressure tests, morphological characterization, etc. Usually comprehensive physical property testing is done by PPMS.
The electrical transport property is one of the most basic and important physical properties of a substance (or material). It reflects the basic physical behavior related to electric charge, such as the law of resistance, Hall resistance changing with temperature, magnetic field, and pressure, and related Physical effects, such as Shubnikov-de Haas quantum oscillation and quantum Hall effect, are one of the most important properties in comprehensive physical properties.
Challenges and Countermeasures of Electric Transport Test
1) Special test conditions. Under normal conditions, the sample to be tested is placed in a low temperature (usually superconducting) and magnetic field environment. The low temperature can reach as low as 0.1mK and the magnetic field can reach as high as 16T. Under extreme conditions, the magnetic field can reach 100T pulsed magnetic field, and the pressure can reach 100GPA. PPMS can provide a test environment under general conditions. In this environment, the thermal effect and the error factors of the test results need to be considered for the test cable connection.
2) Tests that require extremely small or extremely large resistances. Under superconducting conditions, the resistance of the tested sample may be as low as nΩ. In extreme cases, the resistance of the tested sample may be as high as GΩ, and the built-in transport test option of PPMS cannot meet the requirements.
3) It is necessary to test very small voltage, current and differential conductance. At this time, the signal is often submerged in noise, and the built-in test option of PPMS often cannot meet the requirements.
In order to meet the challenges of electrical transport testing, on the basis of PPMS, a high-precision instrument suitable for extremely low-level testing must be added as a necessary supplement. The instrument must have the ability to remove noise. The AC method with the lock-in amplifier as the test instrument and the Delta mode composed of the Tektronix (Keithley) 622x low-level current source/2182A nanovoltmeter combination are two main methods to deal with challenges. The block diagrams of the two methods are as follows :
AC method block diagram Delta mode
Delta mode can provide the measurement and calculation of quasi-DC current reverse technology to eliminate the influence of thermoelectromotive force. Each Delta reading is calculated based on the two voltage measurement results of channel 1; one measures the positive phase of the current source and the other Measure the negative phase, thereby reducing the noise by 1000 times. The AC method and the Delta mode method have their own advantages and complement each other, and they are generally configured during electrical transmission testing. The following figure shows the scope of application of both:
It can be seen from the above two figures that the lock-in amplifier can be used in higher frequency applications, such as pulse testing. However, for resistance testing, the lock-in amplifier is more suitable for testing in the range of 100mΩ ~ 1MΩ, while the Delta mode can test lower-level signals, and is more suitable for resistance testing below 100mΩ and greater than 1MΩ.
Tektronix Transmission Test Solution
In addition to low-level test equipment, SMU is usually configured as a DC excitation source for electrical transmission testing. In special cases, AFG is also needed as an AC excitation source, and an acquisition card or oscilloscope is used to acquire and lock the output signal. If testing the dielectric constant, an electrometer is also required. The study of high-frequency transmission characteristics is the development direction of electrical transmission characteristics testing. When studying high-frequency transmission characteristics, it is necessary to configure an arbitrary waveform generator with a bandwidth of GHz.
Single tested sample test plan:
・24XX or 26XX one
・Optional (one for each)
o 2002 Eight and a half Digit Multimeter
o 6514 or 6517 or 6430 (test dielectric constant)
Simultaneous test plan for multiple tested samples:
For multi-sample testing, you can add a switch array cycle test based on the configuration of a single sample. However, in some cases, such as specific heat and magnetoresistance tests, the same process cannot be tested in cycle mode. In this case, multiple sets of SMUs and low Level test equipment, the number of sets is related to the number of test lines provided by the PPMS lock. The principle is to connect a set of source meters for every four wires and a set of 6221/2182A for every eight wires. The following table shows a typical configuration for simultaneous testing of four sets of PPMS multi-samples in a research institute. In addition to the mandatory and optional requirements for a single sample configuration, this configuration also contains some special-purpose source meters and a set of 4200A-SCS semiconductor parameter tester, used for the test of special tested samples.
High-frequency transport characteristics test program
To test the high-frequency transmission characteristics, it is necessary to add an AWG series arbitrary waveform generator on the basis of the general transmission characteristics configuration. Tektronix provides AWG5200 and AWG70000 series arbitrary waveform generators. The following table shows the main parameters of the Tektronix arbitrary waveform generator:
AWG70001B and AWG70002B AWG5200
・100fA~100mA current output, 1nV voltage test sensitivity, up to 10nΩ resistance measurement sensitivity
・Tektronix unique TSP LINK connects to 6221/2182A, automatically completes the Delta mode test
・Delta mode can reduce noise 1000 times
・Multiple models of high-precision SMUs for excitation source selection
・Leading AWG provides strong support for high-frequency transmission characteristics research
・Generally used in the field of electrical transport testing