Distortion analysis on an improved mask technology for X-ray lithography

Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 90-91).by Kevin P. Pipe.S.B.and M.Eng

Bipolar thermoelectric devices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 124-133).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.The work presented here is a theoretical and experimental study of heat production and transport in bipolar electrical devices, with detailed treatment of thermoelectric effects. Both homojunction and heterojunction devices are considered, and particular attention is given to semiconductor laser diodes. The mechanisms that govern both internal heat exchange and heat transfer between a device and its environment are examined, leading to structures which are optimized for thermal management.by Kevin Patrick Pipe.Ph.D

Emission and detection of surface acoustic waves by AlGaN/GaN high electron mobility transistors

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98689/1/ApplPhysLett_99_243507.pd

Enhanced optical field intensity distribution in organic photovoltaic devices using external coatings

An external dielectric coating is shown to enhance energy conversion in an organic photovoltaic cell with metal anode and cathode by increasing the optical field intensity in the organic layers. Improved light incoupling in the device is modeled using transfer matrix simulations and is confirmed by in situ measurement of the photocurrent during growth of the coating. The optical field intensity in optimized cell geometries is predicted to exceed that in analogous devices using indium tin oxide, both cell types having equivalent anode sheet resistance, suggesting a broader range of compatible substrates (e.g., metal foils) and device processing techniques.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87812/2/233502_1.pd

Organic light-emitting device on a scanning probe cantilever

Organic light-emitting devices (OLEDs) were fabricated on scanning probe cantilevers using a combination of thermally evaporated molecular organic compounds and metallic electrodes. Ion beam milling was used to define the emissive region in the shape of a ring having a diameter of less than 5 μm5μm and a narrow width. Stable light emission was observed from the device at forward bias, with a current-voltage response similar to that of archetypal OLEDs. Based on this device, a novel electrically pumped scanning optical microscopy tool is suggested.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87792/2/111117_1.pd

Temperature mapping and thermal lensing in large-mode, high-power laser diodes

The authors use high-resolution charge-coupled device based thermoreflectance to derive two dimensional facet temperature maps of a λ = 1.55 μmλ=1.55μm InGaAsP/InPInGaAsP∕InP watt-class laser that has a large (>5×5 μm2)(>5×5μm2) fundamental optical mode. Recognizing that temperature rise in the laser will lead to refractive index increase, they use the measured temperature profiles as an input to a finite-element mode solver, predicting bias-dependent spatial mode behavior that agrees well with experimental observations. These results demonstrate the general usefulness of high-resolution thermal imaging for studying spatial mode dynamics in photonic devices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87806/2/201110_1.pd

Computational Sprinting

Although transistor density continues to increase, voltage scaling has stalled and thus power density is increasing each technology generation. Particularly in mobile devices, which have limited cooling options, these trends lead to a utilization wall in which sustained chip performance is limited primarily by power rather than area. However, many mobile applications do not demand sustained performance; rather they comprise short bursts of computation in response to sporadic user activity. To improve responsiveness for such applications, this paper explores activating otherwise powered-down cores for sub-second bursts of intense parallel computation. The approach exploits the concept of computational sprinting, in which a chip temporarily exceeds its sustainable thermal power budget to provide instantaneous throughput, after which the chip must return to nominal operation to cool down. To demonstrate the feasibility of this approach, we analyze the thermal and electrical characteristics of a smart-phone-like system that nominally operates a single core (~1W peak), but can sprint with up to 16 cores for hundreds of milliseconds. We describe a thermal design that incorporates phase-change materials to provide thermal capacitance to enable such sprints. We analyze image recognition kernels to show that parallel sprinting has the potential to achieve the task response time of a 16W chip within the thermal constraints of a 1W mobile platform

Thermal and Electrical Transport in Ultralow Density Single‐Walled Carbon Nanotube Networks

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98216/1/adma_201300059_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/98216/2/2926_ftp.pd

Engineering Temperature‐Dependent Carrier Concentration in Bulk Composite Materials via Temperature‐Dependent Fermi Level Offset

Precise control of carrier concentration in both bulk and thin‐film materials is crucial for many solid‐state devices, including photovoltaic cells, superconductors, and high mobility transistors. For applications that span a wide temperature range (thermoelectric power generation being a prime example) the optimal carrier concentration varies as a function of temperature. This work presents a modified modulation doping method to engineer the temperature dependence of the carrier concentration by incorporating a nanosize secondary phase that controls the temperature‐dependent doping in the bulk matrix. This study demonstrates this technique by de‐doping the heavily defect‐doped degenerate semiconductor GeTe, thereby enhancing its average power factor by 100% at low temperatures, with no deterioration at high temperatures. This can be a general method to improve the average thermoelectric performance of many other materials.Temperature‐dependent modulation doping is demonstrated in a GeTe–CuInTe2 composite material. Temperature‐dependent carrier concentration is achieved by controlling the temperature‐dependent Fermi level offset between the GeTe matrix and CuInTe2 inclusions. An enhanced average power factor over a wide temperature range is demonstrated.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/1/aenm201701623.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/2/aenm201701623-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141881/3/aenm201701623_am.pd

Thermoelectric model to characterize carrier transport in organic semiconductors

A model for the Seebeck coefficient in the regime of hopping transport that includes the effects of Gaussian carrier density of states width and carrier localization allows these parameters to be derived independently of the attempt-to-jump rate, which can subsequently be derived from measured electrical conductivity. This model is applied to prototypical small molecular and polymer organic semiconductors to characterize carrier localization, quantify the role of dopants on the hopping transport parameters, and derive the effective dopant ionization fraction and activation energy.clos