Alexander Govyadinov

New and modified anodic alumina membranes Part I. Thermotreatment of anodic alumina membranes

Abstract Polycrystalline anodic alumina membranes have been prepared by controlled calcination. Phase transformations, porosity changes and conversion of electrolyte impurities incorporated into the anodic alumina lattice were studied as functions of the calcination temperature (up to 1200°C). A comparative IR investigation of hydroxyl cover of the polycrystalline anodic alumina membranes and pure γ- and δ-alumina was carried out. Amorphous anodic alumina films calcined at temperatures up to 800°C with a barrier layer in place (thickness of barrier layer ranged from 5 to 90 nm) were prepared and the permeabilities measured. It is hypothesised that the thin layer of relatively pure and dense alumina of the anodic alumina cell prevents migration of ions, water or small molecules through the barrier layer as well as between the adjacent cells.

Bubble-driven inertial micropump

The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel, or continues to grow axially when it reaches the reservoir. In the non-axial regime, the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section, but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical principles of the pump, a phenomenological one-dimensional model is developed and solved. A linear array of micropumps has been built using silicon-SU8 fabrication technology that is used to manufacture thermal inkjet printheads. Semi-continuous pumping across a 2 mm-wide channel has been demonstrated experimentally. Measured net flow with respect to viscosity variation is in excellent agreement with simulation results.

Polysilicon metal-insulator-semiconductor electron emitter

The flat metal-insulator-semiconductor (MIS) electron emitter is a simple design, allowing easy manufacture. The emitters are relatively insensitive to environment, allowing them to operate in poorer vacuum conditions than are necessary for oxide thermionic or microtip field emitters. In most literature reports, MIS and metal-insulator-metal devices are limited in emission current ( 400pores∕μm2 through which electrons a...

Air cooling limits of 3D stacked logic processor and memory dies

Through-Silicon-Vias (TSVs) enable 3D stack of logic processor and memory dies with significant improvement in latency and energy efficiency of large memory-bound computations. However, additional layers of memory die increase IC package thermal resistance. Thermal management has been identified as a key challenge to achieve high computation power and memory density in the same package. In this paper we present a numerical study on temperature mapping of 3D stacked dies in air-cooled package. We consider DRAM based memory with low power, mid power, and high power logic processors. We study the effect of logic processor power and number of memory dies on the temperature profile. This study provides thermally viable design space of compute-power to memory-size.

One-dimensional model of inertial pumping.

A one-dimensional model of inertial pumping is introduced and solved. The pump is driven by a high-pressure vapor bubble generated by a microheater positioned asymmetrically in a microchannel. The bubble is approximated as a short-term impulse delivered to the two fluidic columns inside the channel. Fluid dynamics is described by a Newton-like equation with a variable mass, but without the mass derivative term. Because of smaller inertia, the short column refills the channel faster and accumulates a larger mechanical momentum. After bubble collapse the total fluid momentum is nonzero, resulting in a net flow. Two different versions of the model are analyzed in detail, analytically and numerically. In the symmetrical model, the pressure at the channel-reservoir connection plane is assumed constant, whereas in the asymmetrical model it is reduced by a Bernoulli term. For low and intermediate vapor bubble pressures, both models predict the existence of an optimal microheater location. The predicted net flow in the asymmetrical model is smaller by a factor of about 2. For unphysically large vapor pressures, the asymmetrical model predicts saturation of the effect, while in the symmetrical model net flow increases indefinitely. Pumping is reduced by nonzero viscosity, but to a different degree depending on the microheater location.

Field emitter with focusing column for atomic resolution storage device

This paper discussed the design and development and fabrication of a focusable electron emitter for atomic resolution storage. The system design includes an electron source with an integrated focusing column and must provide a minimum spot size and maximum efficiency under optimum conditions. Experimental results from the fabricated parts compared well with model spot size predictions.

Novel flat MIS electron emitter

The flat metal-insulator-semiconductor (MIS) electron emitter is a simple design allowing easy manufacture, and is relatively insensitive to environment conditions making operation possible in poor vacuum conditions. A stack of 5000 /spl Aring/ polysilicon/150 /spl Aring/ silicon oxide/50 /spl Aring/ gold deposited on n++ doped silicon showed the best performance. We have observed emission current densities as high as 2-10 A/cm/sup 2/ at efficiencies from 3-10%. The polysilicon serves a dual role. Bumps on the poly surface act as field-enhanced emission sites while the bulk of the film behaves as a ballast resistor that prevents run away emission from any one emission site. The thin gold layer self-assembles into a nano-mesh with >100 pores//spl mu/m/sup 2/ through which electrons escape. Emission theory, including energy distribution and angular divergence of the emitted beams, are discussed.