Cryogenic current-in-plane tunneling apparatus

We have designed and fabricated a cryogenic variable-temperature current-in-plane tunneling apparatus to measure the magnetoresistive properties of unpatterned magnetic tunnel junction wafers as a function of temperature. The wafer is mounted on the cold finger of a liquid helium continuous flow cryostat. The temperature can be continuously varied between 7 and 330 K. We describe the design and fabrication of the micromachined silicon probe head that comprises a comb of 20 measuring and 4 leveling probes. The measuring probes are typically 0.7 μm wide and 1.2 μm thick, with lengths of 10, 7, and 4 μm, and a pitch that varies from 1.5 to 30 μm. The leveling probes are used in conjunction with a tilt stage to adjust the parallelism between the comb and the sample wafer during the approach of the probe head. The probe head is mounted on a nonmagnetic x-y stage, which can access a 22×22mm2 area with a repeatability of ∼1 μm. The first measurements taken at room and cryogenic temperatures are shown. © 2008 American Institute of Physics.