Krishna C. Saraswat - US grants

This project conducts enabling research on virtual prototyping tools for collaborative design, construction, and startup of semiconductor manufacturing facilities. This extends and integrates ongoing research within the Center for Integrated Facilities Engineering and the Center for Integrated Systems at Stanford. The focus is not on design of actual projects or processes, but on the implementation and startup of the factory building and support systems of the manufacturing enterprise. Research is being performed in collaboration with Intel, which is providing specifications and is guiding testing of theory and software. The resulting tools will radically shorten the time to bring new semiconductor facilities on-line.

This FRG/GOALI project is a collaborative effort between researchers at Stanford U., Lehigh U., and Applied Materials, Santa Clara, CA. The project addresses microstructural stability, micromechanics, and electrical properties of materials used in the fabrication of on-chip capacitors incorporating dielectrics such as BaxSr1-xTiO3 (BST) and PbZrxTi1-xO3 (PZT). The aim is to improve understanding of thin film micromechanics, on-chip capacitor electrical performance, and how both electrical and mechanical properties may be modified through thin film microstructural control. Emphasis is on development of a mechanistic understanding of stress relaxation, surface roughening, and film debonding processes occurring during processing of thin film electrodes and diffusion barriers for high-K capacitor applications. Degradation of interfacial contact resistivity and dielectric reliability using patterned capacitor test structures will also be studied. Thermal stress relaxation of electrodes, which affects both adhesion and roughness, will be modified by alloying electrode layers and producing two phase microstructures through internal oxidation. It is anticipated that the research will lead to new strategies for improving the reliability and processing stability of on-chip capacitors that use perovskite-structure high permittivity dielectrics. Research will be performed by a multi-disciplinary, multi-investigator team at Stanford University and Lehigh University. Students and faculty will collaborate with materials researchers and process-integration specialists at Applied Materials, Inc. Joint research activities with AMAT will include sharing of research resources and samples, joint planning of experiments and regular meetings to review progress, visits by students to Applied Materials' laboratories, and mentorship of students by AMAT personnel.
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The project addresses basic research issues in a topical area of materials science with high technological relevance. The basic knowledge and understanding gained from the research is expected to contribute to improving electronic materials performance in current and future device and circuit applications. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. The multidisciplinary (materials science, electrical engineering) and industrially-connected nature of this FRG/GOALI program offers unique educational opportunities for students to experience a teamwork-oriented research environment from both academic and industrial perspectives. The project is co-funded by the Electronic Materials(EM) and Metals(MET) programs in DMR, the Mechanics And Structures of Materials program in ENG/CMS, and the ENG GOALI office.
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Recent scientific progress has isolated nanomaterials that are only 1 to 3 atomic layers thick, with semi- metallic (e.g. graphene), semiconducting (e.g. molybdenum disulphide) and insulating properties (e.g. boron nitride). Unlike well-known bulk materials such as silicon, these atomically thin materials have no dangling bonds, while possessing high electrical and thermal conductivity in the plane of the atomic layers, yet very low conductivity in the direction perpendicular to the atomic layers. In this project, the Stanford team (Pop, Goodson, Saraswat, Wong) will explore fundamental measurements guided by computer simulations, leveraging the unique anisotropic properties of atomically thin materials. The team will also focus on thermoelectric measurements, an area that has received less attention. Applications of this research could include energy-efficient electronics generating little heat, and flexible energy harvesters for wearable sensors and medical devices. Many of the benefits and insights generated from this work could also be applicable to conventional electronics, thus further improving the return on investment for the National Science Foundation, for society, and for education. The project will educate students from high school interns through undergraduate and graduate researchers, who will be exposed to a unique training program at the Stanford Design School. This program seeks to create ?T-shaped? engineers (with technical depth in nanotechnology and lateral ability to collaborate across disciplines). The societal impact of such a new workforce could be just as important as that of the novel nanoscience and nanotechnology enabled by the proposed research.

The technical goals of the research are organized into five tasks: (1) Modeling and simulation of atomically thin materials and devices, guiding their design and assembly. Computational exploration will support the electrical, thermal and thermoelectric experiments. (2) Large scale synthesis and integration of atomic layers into electronic and thermoelectric devices. Atomic layers will be assembled into heterogeneous stacks with controlled angular orientation. (3) Examine and improve electrical inter- faces to atomically thin materials, learning how to connect them to the outside world. The team will leverage doping, and both ?surface? and ?edge? contacts to minimize electrical contact resistance. (4) Thermal and thermoelectric characterization. The researchers will examine thermal interfaces and probe dynamic changes to thermal conductivity, particularly in the cross-plane direction of the atomic layers. These could enable applications like thermal diodes and thermoelectrics. (5) Enable energy- efficient devices and electronics through an approach that ties together the fundamental theory and experiments from Tasks #1-4. The team will examine the possibility of transistors and memory that leverage built-in thermoelectric effects to shift or manipulate hot spots, and that of layered thermoelectric modules for flexible substrates and mobile environments where natural heat sinking is restricted. A key part of the intellectual significance of this project is that it combines expertise from three disciplines: Electrical, Thermal/Mechanical and Materials Engineering. The team leaders have experience collaborating and co-advising students in a multi-disciplinary environment; they will also build on a strong track record of mentoring women and underrepresented minorities (who have gone on to positions in academia and industry) and a strong record of online teaching and learning, including lectures and simulation codes posted on the NSF-sponsored nanoHUB.org. The Stanford environment is uniquely suited for translating fundamental scientific advances to long-term industrial partnerships, and the team will also partner with the Air Force Research Labs for thermoelectric measurements, with Sandia National Labs for atomically thin contacts, and internationally with IMEC (Belgium) and University of Tokyo for material synthesis and experimental approaches for materials integration.