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Device Modeling
and Simulation
We believe
modeling is an art and have shown that an assembly of analogical reasoning,
geometrical interpretation, and interpolation techniques yields physically
meaningful, analytical and compact models. We have also demonstrated how
numerical 2-D / 3-D semiconductor device simulators can be used to assess
novel device concepts, gain insights into physical phenomena and develop
analytical models. Some of our key contributions have been
- On state characteristics of AlGaN / GaN HEMTs
- Breakdown and gate leakage of AlGaN / GaN HEMTs
- Analytical modeling and simulation of nanoscale junctions and FETs
- Analytical modeling and simulation of SiC power MOSFETs
- Solar cell modeling and parameter extraction
- Analytical models for frequency dependent current
spreading in PN junctions
- Calculation of energy bands of nanostructures
- Improvement in the breakdown voltage of superjunctions using the uniform depletion effect
of oxide fixed charges
- Unified Closed-form model of thermionic-field and
field emissions through a triangular barrier
- The design of Field plated HEMTs including novel
structures for improved breakdown voltage
- A compact model for the spreading and coupling
resistances between rectangular and circular contacts
- Equivalent box representation of the non-uniform
channel doping in MOSFETs
- Parameter Extraction of a High Frequency BJT from
Simple measurements on Finished Devices
Prof. Karmalkar has been invited by different reputed
semiconductor research groups in India and the US to bring up their
simulation and modeling activity.
Experimental
Investigations on Processes in Semiconductor Technology
Electrochemical metallization
processes have been investigated leading to the development of the
following :
- Selective plating of N-type and P-type areas on a
silicon surface by pulse electroplating
- A new solution to activate polished silicon
surfaces for obtaining adherant electroless plating
- New insights into palladium activation and electroless plating mechanisms
- An all-plated process for bump metallization of
silicon
The work on
activation and electroless plating has attracted
the attention of other researchers who have subsequently shown the utility
of the new solution in deposition of palladium nano-particles.
The work was also presented as an invited talk in the Spring 2006 meeting
of International Society of Electrochemistry in Singapore.
Indigenous Development
of Imported Devices
We have undertaken
projects requiring comprehensive application of engineering principles to
practical problems. One such venture involved indigenous development of the
technology of the imported axial lead glass packaged high-Q VHF-UHF tuning
diodes. This initiative, undertaken by Prof. Karmalkar
on loss of pay leave from the institute, was one of the factors which
encouraged IIT Madras to amend its leave rules by including a paid leave
for entrepreneurial efforts. It also provided an opportunity to work in
different laboratories, industries and institutions of the country in what
could be termed as a "technology pilgrimage". Subsequently, we
have actively pursued indigenous development of imported semiconductor products
in collaboration with industries. A manufacturing process for KSC 1393
Tuner transistor used in high frequency tuning applications has been
developed and put into production, as a part of a consultancy project
granted by Bharat Electronics Ltd, (BEL) Bangalore. Encouraged by this
success, BEL has entered into a bigger consultancy project for developing
power MOSFETs.
MEMS / Microfluidics / Nanotechnology
An active, normally-closed piezoelectric microvalve
useful for automated drug delivery or control of fluids in microreactor systems has been fabricated. The microvalve has dimensions of 19 x 19 x 7 mm, an inlet
diameter of 200 um, a dead volume of 0.33 ul and
has a steady-state flow-rate of about 240 sccm.
It is controlled by voltages in the range of 100-300 V.
A systematic method for moulding microchannels in PDMS without using complicated systems
or costly materials has been developed. Several experiments have been
conducted on DNA separation in PDMS channels. The sample volume was 5 ul in early experiments but could be reduced to only
0.5 ul of the sample, by gaining insight into
important factors to be considered while designing a micro-electrophoresis
system.
Formation of protein gradient on PDMS using silicon microchannels of 10 mm - 30 mm length and 15 um - 500
um width terminating in pits of 0.25 cm2 - 1 cm2 area
has been studied. The PDMS substrates were placed on the microchannels, through which a protein solution was
made to flow by capillary action after injection into the filling pit. The
protein gradient detected on PDMS substrate showed that
channels with smaller width and depth and are necessary to form
stronger gradients over shorter channel length.
Education
New treatments have been developed to teach difficult
semiconductor concepts in the classroom. These treatments aim at enhancing
the student's comfort level and theory building capabilities. Some of our
key contributions published in IEEE Trans. Education are
- Appealing analogies to illustrate
- the quantum mechanical nature of carrier
scattering
- the difference between quasi-static and rigorous
approaches to junction capacitance calculation
- A unified perspective to
- drift, diffusion and thermoelectric currents
- depletion and diffusion capacitances
- An effective and efficient introduction to semiconductor
device modelling
Our research on
education also shows how proper introduction of a topic with carefully
chosen illustrations and mnemonics can improve the teaching-learning
process and how such improvements can be assessed.
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