Design of Vibration Tolerant Microelectrodes and Field Effect Characterization of MoS2

Kristoffer Gram Kalhauge

Research output: Book/ReportPh.D. thesis

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Abstract

Since the industrial revolution metrology has played and important role behind the scene. With the invention of the transistor and later the development of modern integrated circuits, that role has only become more and more important. One of the key methods in electrical characterization is the four-point measurement. Where four contacts are made to a sample, these are then used to pass a current between two of them and measure the corresponding potential drop across the other two. As the critical dimension shrunk, first below a micrometer and then to the nanometer-scale, the traditional four point probe became increasingly unsuited for the job. Micro four-point probes, consisting of electrodes on the micrometer scale, have since been a viable and often superior alternative.
Several different measuring methods have been developed using the micro four-point probe. Including micro Hall, sheet resistance measurements and measurements on ultrashallow junctions.
In this thesis the governing mechanics of cantilevers, consisting of two beams joint at an angle, is derived. This is then used to optimize an existing cantilever to achieve a higher tolerance to vibrations. In order to do this an expression for the vibration tolerance is derived and tested. Based on the existing cantilever, two new designs are found. Not only does the new designs improve the mechanical performance by a factor of two or more. But they achieve this while either keeping the minimum pitch or decreasing it from 1.5µm to 1.1µm.
This thesis also presents the use of micro four-point probes to perform field effect measurements on two dimensional materials. Only a single crystal basis thick, these materials form large continues flakes that in bulk are held together by van der Waals forces. However, it is their properties as a single or a few layer materials that is of interest in the development of electronics. The most known of these is graphene. With a high mobility and semi-metallic electron behavior. Graphene has seen its introduction in everyday electronics already. Due to its conductive nature its uses in many devices are limited. Alternatively, other materials such as transition metal dichalchoginites show interesting physical attributes. And, the one studied in this thesis (molybdenum disulfide - MoS2) is a semiconductor, making it interesting as a transistor material. To measure on this material a microRSP-M200 tool from CAPRES, was modified so that it could source voltage in DC.
On this modified setup field effect measurements were successfully performed, allowing for the measurement of threshold voltage and field effect mobility on the material. A precision of the measured current within the same engage of 10% was achieved.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages132
Publication statusPublished - 2020

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