Miltiadis K. Hatalis

Macroelectronics: Perspectives on Technology and Applications

Flexible, large area electronics - macroelectronics - using amorphous silicon, low-temperature polysilicon, or various organic and inorganic nanocrystalline semiconductor materials is beginning to show great promise. While much of the activity in macroelectronics has been display-centric, a number of applications where macroelectronics is needed to enable solutions that are otherwise not feasible are beginning to attract technical and/or commercial interest. In this paper, we discuss the application drivers and the technology needs and device performance requirements to enable high performance applications to include RF systems.

Polysilicon TFT technology for active matrix OLED displays

The integration of active matrix polysilicon TFT technology with organic light emitting diode (OLED) displays has been investigated with the goal of producing displays of uniform brightness. This work identifies and addresses several process integration issues unique to this type of display which are important in achieving bright and uniform displays. Rapid thermal processing has been incorporated to achieve uniform polysilicon microstructure, along with silicides to reduce parasitic source and drain series resistance. Using these processes, TFT drain current nonuniformity has been reduced below 5% for 90% of the devices. This work also introduces transition metals to produce low resistance contacts to ITO and to eliminate hillock formation in the aluminum metallization. These processes, along with spin on glasses for planarization, have been used to produce functional active matrix arrays for OLED displays. The final array pixel performance is also presented.

Raman spectroscopy of amorphous and microcrystalline silicon films deposited by low‐pressure chemical vapor deposition

In this work we used Raman spectroscopy to investigate the structural characteristics of as‐deposited amorphous and micro‐crystalline silicon films. For amorphous silicon films, the order (or disorder) of the silicon network was quantified using properties of the Raman spectra that were related to key deposition conditions. We found that a strong relationship exists between the structural order of the silicon matrix and the deposition temperature and deposition rate. A quantitative model was proposed relating the intensity ratio of transverse optical phonon peak to longitudinal optical phonon peak to the surface diffusion length, a parameter that was calculated from available data. It was found that optimization of the as‐deposited silicon microstructure is possible by selecting deposition conditions yielding peak–ratio values in the vicinity of 0.53. For as‐deposited micro‐crystalline silicon films, Raman spectroscopy was used to estimate the initial crystalline fraction of the film and monitor the cryst...

Tactile displays : Overview and recent advances

Abstract Tactation is the sensation perceived by the sense of touch, and is based on the skin’s receptors. Touch is a common medium used by the general population and the sensory impaired. Tactile substitution can be used by the blind or deaf in order to: (a) enhance access to computer graphical user interfaces and (b) enhance mobility in controlled environments. The skin nerves can be stimulated through six types of receptors by mechanical, electrical, or thermal stimuli. Modalities, such as vibration and pressure, can stimulate these receptors. Advances in tactile communication using implementations of the actuating devices have been developed via several new technologies. These technologies include static or vibrating pins, focused ultrasound, electrical stimulation, surface acoustic waves, and other. This paper is a review of the state-of-the-art in the physiological and technological principles, considerations and characteristics, as well as latest implementations of microactuator-based tactile graphic displays. We also review fabrication technologies, in order to demonstrate the potential and limitations in tactile applications.

Structure of As‐Deposited LPCVD Silicon Films at Low Deposition Temperatures and Pressures

In this work we studied the effect of the deposition temperature, total pressure, source gas dilution, and deposition rate on the structure of the as-deposited silicon films. Depositions were performed by low pressure chemical vapor deposition (LPCVD) in the temperature range of 530 to 600 o C and in the pressure range of 2 to 300 mTorr. For a fixed deposition temperature a phase transition from polycrystalline to amorphous silicon was shown to occur when the deposition rate exceeded a critical value

Towards a palladium micro-membrane for the water gas shift reaction: microfabrication approach and hydrogen purification results

A novel palladium-based micromembrane is reported that can be used for hydrogen gas separation in a miniature fuel processor for micro fuel cells. The micromembrane structure is built in a silicon substrate, using standard MEMS microfabrication processes. Four layers, viz. copper, aluminum, spin-on-glass (SOG) and palladium form the composite membrane. Copper, aluminum and SOG layers provide structural support for the palladium film. Copper can act as catalyst in the water gas shift reaction that converts unwanted carbon monoxide gas into hydrogen. Palladium is used to separate hydrogen from other gases present. The micromembrane selectively separates hydrogen from a 20:80 hydrogen:argon gas mixture by weight even at room temperature. The diffusion of hydrogen through palladium is enhanced at higher temperatures and pressures, closely following the predictions from Sieverts law. Future applications of this micromembrane for simultaneous water gas shift reaction and hydrogen separation are discussed.

Deposition and Crystallization of a‐Si Low Pressure Chemically Vapor Deposited Films Obtained by Low‐Temperature Pyrolysis of Disilane

In this work we have studied the deposition and crystallization of silicon films initially deposited in the amorphous phase by thermal decomposition of disilane and subsequently crystallized upon a low temperature thermal anneal. Experiments were performed over a wide range of deposition conditions. The grain size of the crystallized films was found to depend upon the deposition conditions; particularly it was found to increase monotonically with increasing deposition rate, while a nonmonotonic behavior was observed with respect to the deposition temperature. For films deposited with similar deposition rates, in the temperature range of 450 to 550 o C, a maximum in the grain size was observed at 470 o C

A microreactor for in-situ hydrogen production by catalytic methanol reforming

A detailed study of the theoretical and experimental issues involved in the design and operation of a silicon-based methanol microreformer is presented in this paper. Thermal simulations for heat loss from the reformer chip and calculations involving the endothermic heat effect of the reforming reaction were carried out to estimate the total power requirement for continuous operation of the reformer. Micromachining technology was utilized to fabricate a prototype silicon microchannel based reformer of channel cross-section 1000μm x 230μm with a copper layer of thickness ∼ 33nm as catalyst. The reactor chip was interfaced with the tubing for reactant and product transport using a stainless steel housing machined to exact dimensions and flexible graphite pads to provide gas-tight seals and excellent thermal contact between the chip and the housing for external heating of the reformer. Runs of this prototype microreformer were carried out using a custom made experimental setup for generation of the reactant mixtures, temperature control of the microreactor and online measurement of the product gas composition. Results from test runs of the microreformer are presented and strategies for improving the hydrogen yield are discussed.

Lateral polysilicon p+–p–n+ and p+–n–n+ diodes

Abstract Lateral polysilicon p+–p–n+ and p+–n–n+ diodes are fabricated and their electrical characteristics, such as ON-resistance, ideality factor and reverse current, are studied as a function of the polysilicon microstructure, the type and amount of doping in the lightly doped region and the length of the lightly doped region. Increasing the polysilicon grain size reduces the ON-resistance. The ON-resistance decreases while the reverse current increases with an increase in the amount of doping in their lightly doped region. The ON-resistance is higher and the reverse current is lower in diodes having p-type lightly doped regions. With an increase in the length of the lightly doped regions, the ON-resistance increases, while the reverse current does not change. The ideality factor does not depend upon the length of the lightly doped region, type of doping in this region and the grain size of polysilicon. The experimental observations are explained using a combination of field enhanced emission and a formulation that considers the effect of the grain-boundary segregation of dopants.

Polysilicon VGA active matrix OLED displays-technology and performance

The first VGA polysilicon active matrix organic light emitting diode (AM-OLED) display will be presented. The goal of this work is to investigate the technology and performance of polysilicon active matrix OLED displays along with a new driving method.