Indian Instituite Of Technology ? Bombay
IIT Bombay, set up by an Act of Parliament, was established in 1958, at Powai, a northern suburb of Mumbai. Today the Institute is recognised as one of the centres of academic excellence in the country. Over the years, there has been dynamic progress at IIT Bombay in all academic and research activities, and a parallel improvement in facilities and infrastructure, to keep it on par with the best institutions in the world. Institutes in positions of excellence grow with time. The ideas and ideals on which such institutes are built evolve and change with national aspirations, national perspectives, and trends world - wide. IIT Bombay, too, is one such institution.
Department Of Electrical Engineering
The EE department at IIT Bombay has been active in teaching and research since its inception in 1957. Currently, about 45 faculty members are engaged in research in the areas of Communication and Signal Processing, Control and Computing, Power Electronics and Power Systems, Microelectronics and VLSI design, and Electronic Systems.
The department has academic programmes with about 320 undergraduate and 200 postgraduate students. The department is equipped with the latest experimental and computational facilities for taking up R & D and consultancy activities in various fields.
CTARA
Since its inception in 1985, Center for Technology Alternatives for Rural Areas (CTARA) at IIT-Bombay is involved in design and development of technologies relevant to rural areas. The current working areas of CTARA include farm machinery, food processing, low cost housing, renewable energy, water management, rural industry etc. The CTARA carries out its programmes through full time research assistants, visiting experts and associated faculty members from different disciplines at IIT. Presently the undergraduate and graduate students from other engineering or applied science disciplines participate in CTARA activities as a part of thesis or project requirement.
CONTENTS
1. Introduction
2. Cooling Using Microchannels
3. Two Phase Flow in Microchannels
4. Annular Flow Model
5. Fabrication of Silicon Chip
6. Lithography
7. Photolithography
8. Lithography Module
9. Etching
10.Conclusion
11.Scope for Future work
12.References


1. INTRODUCTION
Power densities encountered in microelectronic equipment have increased tremendously due to progress in semiconductor technology. Integrated circuits in the near future are expected to have such large power densities, that traditional air cooling will no longer be sufficient to cool them. The thermal design goal is to limit the magnitude of chip temperature rise above ambient temperature in order to ensure satisfactory electrical circuit operation and reliability. For optimal performance and lifetime of these devices, more efficient cooling techniques will be required.
Microprocessors, in the near future, are expected to have a requirement for removing a very large amount of heat from a small area. Conventional air cooled heat sinks will no longer be sufficient to cater to this requirement. Heat transfer to fluids flowing through microchannels is being looked upon as a promising solution to this problem. Hence, a thorough understanding of heat transfer in microchannels has become a necessity.
Our knowledge of macro-scale heat transfer cannot in general be directly applied to heat transfer in microchannels. Experimentation and modeling studies are being carried out by various researchers around the world to obtain a better understand of micro-scale heat transfer. There is a need for the development of better models and correlations to explain experimental observations related to microflows. Annular flow is a flow pattern observed by several researchers in microchannels. Annular flow model has been studied, modified and extended for obtaining the pressure distribution and for handling non-uniform heating along the microchannel.

2. COOLING USING MICROCHANNELS
A very promising solution for cooling microchips is by heat transfer to single phase and boiling fluids flowing through microchannels. To cool a small device having a large power density, we require a very large heat transfer coefficient between the device and the cooling fluid. From our experience with macro-scale flows, we know that in a fully developed laminar flow of a liquid through a tube with uniform surface heat flux, the Nusselt number is a constant. This implies that, the heat transfer coefficient is inversely proportional to the hydraulic diameter. Thus, the heat transfer coefficient is expected to have a very large value when the hydraulic diameter of the channel is in the range of micrometers. However, such an increase will come at the cost of a significant increase in pressure drop across the channel.
3. TWO PHASE FLOW IN MICROCHANNELS
It has been claimed by Goodson et al. [3] that boiling heat transfer in microchannels requires less pumping power than single-phase liquid convection to achieve a given heat sink thermal resistance. Also, using a two phase flow helps to eliminate large temperature variations within the device. Unless a very large flow rate is used, this is difficult to achieve using a single phase flow. A large flow rate will invariably lead to a large pressure drop which requires more pumping power, may generate more noise and requires bulkier packaging.
4. ANNULAR FLOW MODEL
Annular flow is a regime that has been observed by many researchers in microchannels. Qu and Mudawar [8] have attempted a model of annular flow that is described in brief below.
In an annular flow, the vapor phase flows along the center of the channel and is surrounded by a thin film of liquid along the channel walls. The vapor phase, thus, forms a continuous vapor core in the center of the channel. Liquid droplets are entrained in the vapor core. Mass is continuously exchanged between the liquid film and vapor core in the direction of the fluid flow.

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