[BNC-all] Preliminary examination announcement - Sambit Palit

[Sambit Palit]

Dear all,

You are invited to the presentation for my Preliminary exam, the details 
of which are as follows. Coffee and cookies will be provided.

Title: Charging and Transport in Amorphous Dielectrics and Reliability 
Implications for RF-MEMS

Date:     01/29/2013
Time:     02:00 PM
Venue:    BRK 1001

Abstract:
Thin film dielectrics have broad applications, and the performance
degradation due to charge trapping in these thin films is an important
and pervasive reliability concern. Historically, charge transport
through dielectrics has been presumed to be either bulk dominated
(Frenkel-Poole (FP) emission) or to be contact dominated
(Fowler-Nordheim tunneling), dependent on the dielectric thickness. We
develop a comprehensive dielectric charging modeling framework which
solves for the transient and steady state charge accumulation and
leakage currents in an amorphous dielectric, and show that for most thin
film dielectrics in commercial use, the conventional assumption of FP
dominated current transport is incorrect, and may lead to false
extraction of dielectric properties. In order to correctly characterize
dielectrics from their steady state leakage current characteristics, we
propose an improved technique based on an analytical approximation of
the dielectric charging model. We further show that our model replicates
measured transient leakage characteristics in Silicon Nitride more
accurately, given defect energy levels are known from first-principles
calculations. Next, we study Radio Frequency Microelectromechanical
Systems (RF-MEMS) capacitive switches as one of the target applications
of these thin film dielectrics. Charge accumulation in dielectrics in
RF-MEMS capacitive switches result in temporal shifts in actuation
voltages, eventually resulting in failure due to stiction. Analysis and
design of electromechanical actuators has historically been done on a
case-by-case basis. We propose fundamental scaling relationships in
electromechanical actuators in general, which are independent of
specific physical dimensions and material properties. The scaling theory
offers an intrinsic classification of all electromechanical actuators
and consequently reduces the problem of analysis/design of complex
electromechanical actuators to determining a few scaling parameters
associated with specific geometry-classes. Finally, we propose a novel
fully electronic, resonance based characterization technique for RF-MEMS
capacitive switches to quantify degradation due to dielectric charging,
which overcomes several limitations in conventionally used methods. The
proposed technique also opens up possibilities for large scale
parallelization for technology qualification and in-situ electronic
degradation monitoring. In the future, we wish to generalize the theory
of dielectric charging and degradation physics to polymer dielectrics.
Even though polymer dielectrics are widely used as inter-layer
dielectrics, diffusion barriers and passivants in conventional
fabrication processes, their degradation is often modeled empirically.
The techniques developed in this preliminary report will help explain
and solve some of the long standing puzzles in this field.


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