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Hall Test
1. The probe station Hall test leverages the probe station's micrometer-level precision in positioning and contact capability to apply a stable magnetic field and current to semiconductor samples. By measuring the Hall voltage, this non-destructive testing method allows researchers to accurately determine key electrical parameters such as carrier concentration and mobility.
(1) High-Precision Positioning and Contact: The probe station is equipped with a high-precision probe holder and advanced motion mechanisms, such as X-Y-Z three-axis linear movement, achieving positioning accuracy better than 1 μm. This allows for precise placement of the probe onto the sample’s test point, ensuring reliable electrical contact with the sample surface—minimizing contact resistance and measurement errors. Additionally, the probe station and probes are constructed from non-magnetic materials to prevent interference with Hall effect measurements.
(2) Stable Magnetic Field System: The magnetic field is one of the key elements in Hall testing, requiring a stable and adjustable magnetic field provided by components such as an electromagnet, a magnetic field power supply, and a circulating water-cooling unit. For instance, the EM-series electromagnets feature a water-cooled coil design that ensures both stability and uniformity of the magnetic field, enabling the generation of horizontal magnetic fields at various air gaps—such as 2.2 T at a 20 mm air gap.
(3) Precise Temperature Control: For tests requiring the study of how temperature affects the Hall effect, the probe station must feature accurate temperature-control capabilities. For instance, the Hall Low-Temperature Probe Station HCP621G-PMH can precisely regulate temperatures ranging from -190°C to 600°C, with temperature stability as high as ±0.05°C (>25°C) and ±0.1°C (<25°C). Additionally, it can be equipped with a protective gas supply to prevent sample frost formation at low temperatures or oxidation at elevated temperatures.
(4) Efficient Measurement and Data Analysis Software: Paired with dedicated measurement and data analysis software, this tool automatically collects and processes measurement data, swiftly calculating parameters such as the Hall coefficient, carrier concentration, and mobility. It also generates relevant characteristic curves—like I-V, R-H, and R-T curves—enabling users to easily analyze and conduct research.
2. Procedure for performing Hall measurements using a probe station.
(1) Preliminary Preparation: Verify that the probe station, magnetic field system, low- and high-temperature chamber (if required), source meter, and other equipment are properly connected and calibrated. Secure the semiconductor sample onto the sample stage, ensuring the test area is free from any contamination. Based on the sample size and the positions of the test points, install the appropriate non-magnetic probes—typically 4-pin or 6-pin probes.
(2) Sample Positioning and Probe Contact: Use the microscope imaging system on the probe station to locate the sample test point. Then, precisely control the micrometer-level stage to move the probe until it makes accurate contact with the test point, ensuring stable contact resistance (typically by monitoring the source meter’s conduction status).
(3) Test parameter settings: In the control software, define the test conditions, including the applied current value, magnetic field strength (fixed or continuously varying range), temperature parameters (room temperature, high/low temperatures, and stabilization time), and select the measurement mode (e.g., DC Hall, FastHall, etc.).
(4) Environmental and Magnetic Field Activation: If high- or low-temperature testing is required, close the sample chamber and flush it with a protective gas (such as nitrogen). Then, activate the temperature control system and allow it to reach and stabilize at the target temperature. Next, turn on the magnetic field system, ramp up to the set magnetic field strength, and maintain a uniform, stable level throughout the process.
(5) Data Acquisition and Recording: Initiate the measurement program, and the equipment will automatically apply current and magnetic fields while simultaneously collecting data such as Hall voltage and longitudinal voltage. Some systems also support real-time plotting of characteristic curves like R-H and R-T, and once completed, the raw data is saved for future analysis.
(6) Post-Test Processing: Sequentially turn off the magnetic field, temperature control system, and power supply, then remove the sample. Use analytical software to calculate key parameters such as carrier concentration and mobility, and generate a test report.
4. Summary of the Hall Test Procedure:
(1) Core Technology Architecture
- Precision Positioning and Contact System: The probe station body is constructed using non-magnetic materials, equipped with an X-Y-Z three-axis micrometer-level displacement probe stage (positioning accuracy better than 1 μm) and compatible probes such as tungsten or beryllium-copper needles. Combined with a thousands-fold magnification microscopy system, this setup enables precise crimping onto tiny test points, ensuring stable contact resistance.
- Controllable Magnetic Field Supply System: Composed of electromagnets (such as the C-type EM series), high-precision power supplies, and water-cooling units, this system delivers a stable and adjustable magnetic field (e.g., 1.5T at a 40mm air gap, 2.2T at a 20mm air gap). It supports smooth magnetic field scanning and reversal, meeting the diverse magnetic field requirements for testing various materials.
- Environmental and Interference Control System: Utilizing an airtight chamber filled with protective gas (to prevent oxidation), integrated dry air ducts (to avoid low-temperature frost buildup), and a Permalloy shielding enclosure, this system minimizes the impact of temperature fluctuations and electromagnetic interference (EMI) on testing. Additionally, both the test bench and its components are made from non-magnetic materials to eliminate any magnetic field disturbances.
- Automated Measurement and Analysis Module: Integrates testing algorithms such as the Van der Pauw method, employing a dual-reversal technique for current and magnetic fields to eliminate errors like thermoelectric effects and offset voltages. Paired with dedicated software, it automatically collects data, instantly calculates parameters like the Hall coefficient and mobility, and generates characteristic curves in real time.
(2) Core Application Value
- A critical support for R&D and production: Covering fields such as semiconductor materials, nanomaterials, and Hall sensors, providing quantitative data to guide material selection and process optimization—for instance, using mobility testing to assess the uniformity of semiconductor doping.
- Dual Assurance of Cost Reduction and Efficiency Enhancement: Non-destructive testing allows for the repeated characterization of a single sample’s temperature and magnetic-field response properties, minimizing sample wastage. Meanwhile, an automated process reduces the testing time per sample to just 1–2 minutes, significantly boosting overall testing efficiency.
- Versatile multi-scenario compatibility: Can be paired with high- and low-temperature control systems (-190°C to 600°C) to enable testing across a wide temperature range. It can also adapt to cutting-edge research scenarios like the quantum Hall effect through magnetic field adjustments, seamlessly meeting both fundamental scientific research and industrial testing needs.