Charge Transport Laboratory
Cook Hall, 1163
Laboratory Director: Mark Hersam, MSE
The Charge Transport Laboratory includes equipment to perform DC electrical measurements on a wide variety of samples, including electrical conductivity measurements and device characterization. A new four-point probe station has been installed, which includes high-precision movement, a 120X microscope for probe positioning, a vacuum chuck, and a full light enclosure. A fixed inline four-point probe is also available for simplified electrical conductivity measurements on bulk samples or thin films. Two Keithley 2400 source meters are provided for the measurements and can be operated using custom software on the connected PC.
Typical measurements performed include sheet resistance measurements on thin films, conductivity measurements of nanopatterned regions, field-effect transistor characterization, and electronic characterization of light-sensitive samples.
EQUIPMENT:
1. Ambient Probe Station:
Cascade Microtech probe station with 7 probes connected with two Keithley source-meters controlled by home-built LabVIEW programs. It has a microscope for probe positioning, a vacuum chuck, and a full light enclosure Also attached is a 4-probe van der Pauw measurement system for thin films.
The probe station is currently located in Cook 2014. The probe station can perform DC electrical measurements on a wide variety of samples, such as thin film transistors, semiconducting and metallic films, and heterojunctions.
2. Vacuum Cryogenic Probe Station:
Model CRX-4K from LakeShore Cryogenics. Measurements can be done in vacuum (2 x 10^-5 Torr) at variable temperature from 350 K down to 7 K. It has 5 electrical probes (triax) and an optical fiber that can be used to illuminate spectral-resolved Xe lamp or lasers (465 nm, 515 nm, 785 nm, 1550 nm) for photocurrent measurements. There is an option of microwave measurements (20 GHz) with GSG probes. There are three Keithley source-meters, a lock-in amplifier, a spectral analyzer, a Tek 4200 SCS system, signal generators, and an oscilloscope. All equipment are controlled by LabVIEW programs.
Typical samples include field-effect transistors, phototransistors, heterojunctions, high speed circuits, and conducting films.
3. Automated Probe Station:
This probe station is an M150 Benchtop Station by Cascade Microtech, Inc. This specializes in automated measurements of array of devices on full wafers. The stage has 155 mm of high precision XY motion and 5 mm of Z-motion as well as a vacuum chuck. A Leica S6 D StereoZoom Microscope with up to 120X magnification and lighting is included for accurate positioning of the tungsten probes. The probe station is enclosed in a light tight enclosure and is connected to two Keithley 2400 SCS controlled by a PC. LabVIEW software is provided for common electrical measurements. The inline four-point probe consists of four tungsten probes with 1 mm separation and spring action for making contact with samples. The coarse Z-position of the probes is also adjustable for measuring larger samples.
Typical samples include full wafer with series of devices (100s) patterned in a regular array. The automated positioning software can accept array design. The user does not need to be present during all measurements.