COMPARATIVE Ashishkumar Jaiswal Electronics and Telecommunication Thakur College

 

COMPARATIVE ANALYSIS AND DESIGN OF OSCILLATOR USING
MESFET

 

 
 
Ashishkumar Jaiswal
Electronics and
Telecommunication
Thakur College of Engineering and
Technology,Mumbai
[email protected]

Suryaprakash patel
Electronics and Telecommunication
Thakur College of Engineering and
Technology,Mumbai
[email protected]

            Shubham Singh
Electronics and Telecommunication
Thakur College of Engineering and
Technology,Mumbai
[email protected]

Mrs. Anvita Birje
Assistant Professor
Electronics and Telecommunication
Thakur College of Engineering and
Technology,Mumbai
[email protected]

 

 

ABSTRACT-MESFET stands for metal–semiconductor field-effect transistor. It is quite similar
to a JFET in construction
and terminology. The difference is that instead of using a p-n junction for a
gate, a Schottky (metal-semiconductor) junction is used.
MESFETs are usually constructed in compound semiconductor technologies lacking
high quality surface passivation such as GaAs, InP, or SiC, and are faster but
more expensive than silicon-based JFETs or MOSFETs. Production MESFETs are operated up to approximately
45 G commonly used for microwave frequency communications and radar. The first MESFETs were developed in 1966, and a year
later their extremely high frequency RF microwave
performance was demonstrated.

                                   

 

INTRODUCTION

The technology of metal–semiconductor field effect
transistor (MESFET) based on GaAs substrate has undergone a rapid development
in recent years. The use of GaAs substrates for IC circuits offers some
outstanding advantages over the traditional Si substrate, especially in the
area of high frequency and high speed microwave circuits. Its application
extends to low noise preamplifiers and linear amplifiers, oscillators and
mixers in communication networks due to some of its outstanding physical properties,
such as high cutoff frequency (more than 10 GHz for 1 ?m gate length) and high
electron mobility. Furthermore, GaAs circuits are suited for optoelectronic
applications due to its direct-bandgap property which can be grown with semi-insulating
bulk conductivity.rapid thermal annealing equipment have made the fabrication
for advanced GaAs MESFET simpler and lower cost.In the operation of a MESFET,the
electrical conduction between the source and drain is modulated by a bias
applied to the gate. The Schottky barrier formed by metal-semiconductor
junction makes the gate isolated to channel. Thus, by controlling the doping
level of the channel it is possible to obtain enhancement- or depletion-mode
transistors. The switching characteristics of such digital inverters made from
GaAs MESFET’s are comparable, even much superior than those the Si-based
digital inverters. The typical intrinsic time delay for such kind of inverters
can be lower than 100 ps for 1-?m gate length devices. Conventional amorphous
silicon (a-Si) has few drawbacks, such as low pixel brightness and requires
high field effect mobility for high drive currents. Recently, ZnO has developed
as a substitute material for TFTs under wide area operations

7. It is a direct band gap semiconductor of II-VI
semiconductor group (~3.3-3.4 eV), which possesses high electron mobility 8,
high exciton binding energy~60meV 9 and can easily be n-doped. Due to large
bandgap, it has higher breakdown voltage and can sustain large electric fields
and hence, can be used for high temperature and high power operations.
Moreover, ZnO based TFTs have been intensively studied due to their high
transparency, non-toxicity as well as their consistency with glass and plastic
substrates10. The three main parameters that determine the performance of
TFTs are on-off current ratio, field effect mobility and threshold voltage.
Significant efforts have been made to achieve good performance through these
parameters in this paper. The process of scaling in thin film transistor has
often resulted in higher device density, smaller device configuration and
better performance. The industry roadmap estimates the barriers of continuous
scaling will be due to practical technology as well as physical limitations
11. So, the need arises for alternative device structures. Thus,

 

 

 

 

this paper aims to study the effect of varying channel
lengths 50nm down to 30nm on the I-V characteristics by means of simulation
study for ZnO thin film transistors. The paper is ordered as follows: Section
II presents proposed

device structure of bottom gate ZnO TFT.
Section III deals with results and discussion section which further includes
the I-V characteristics curves at different technology nodes. Section IV
presents study and comparison of simulated results with the theoretical results
using Matlab and finally conclusion is drawn in section V.

 

LITERATURE
SURVEY

 

This section represents the papers presented
and published by various people related to Attendance monitoring systems.

 

  (A) GaAs MESFET Large Signal Oscillator Design-K.M.
Johnson

 Techniques for
large signal GaAs MESFET oscillator design are described which do not require
repeated large signal measurement. In the first technique, small signal
S-parameter measurements are used with a computer program to compute the
packaged and mounted device equivalent circuit. Large signal measurements are
made to determine a mathematical relationship between only those parameters
which vary under large signal conditions. These relationships are included in the
computer program. Then, once the equivalent circuit has been computed from the
small signal S-parameter measurements, those parameters varying under large
signals are incrementally altered until large signal S parameters are obtained
which correspond to maximum oscillator output power. These values are used to
calculate embedding element values for six oscillator topologies. A coaxial
cavity FET oscillator was built and tested using the large signal design
theory, and it substantially verified the design technique. The second design
technique is based on the fact that S/sub 21/

varied more than other S parameters under large signals.
By making design calculations based on S/sub 21/ reduced to the point
corresponding to maximum oscillator power, it was possible to get usable design
information for an FET oscillator.

 

(B)Fabrication of
GaAs MESFET Ring Oscillator on MOCVD Grown GaAs/Si(100) Substrate -Toshio
Nonaka, Masahiro Akiyama, Yoshihiro Kawarada and Katsuzo Kaminishi Japanese
Journal of Applied Physics, Volume 23, Part 2, Number 12

GaAs MESFET crystal oscillators were successfully
fabricated on silicon substrate. GaAs epitaxial layers were grown directly by
MOCVD on Si(100) substrate. A typical transconductance of 200 mS/mm was
observed for the FET of 1.0 µm × 10 µm gate. A minimum propagation delay time
of 51 ps/gate at a power dissipation of 1.1 mW/gate was observed for an E/D
gate ring oscillator with gate length of 1.0 µm.GaAs MESFET ring oscillators
were successfully fabricated on silicon substrate. GaAs epitaxial layers were
grown directly by MOCVD on Si(100) substrate. A typical transconductance of 200
mS/mm was observed for the FET of 1.0 µm × 10 µm gate. A minimum propagation
delay time of 51 ps/gate at a power dissipation of 1.1 mW/gate was observed for
an E/D gate ring oscillator with gate length of 1.0 µm1. 

 

 

(C)Low frequency
noise physical analysis for the improvement of the spectral purity of GaAs FETs
oscillators-J.Graffeuil.Tantrarongroj,.J.F.Sautereau

Low frequency (L.F.) noise in GaAs FETs was investigated
both theoretically and experimentally. The main contribution to the overall
noise at frequencies over 103 Hz was found to be flicker noise generated in the
gradual region of the channel.A new simple relationship is proposed to derive
the noise voltage intensity referred back to the input at normal operating
conditions: it is reported that this noise spectral intensity does not depend
on bias voltages for micrometer or submicrometer devices. This relationship
provides a fast and easy way for assessing devices for their L.F. noise: an
improvement in the spectral purity of GaAs FETs oscillators designed with low
L.F. noise FETs is reported2

.

(D)Design of GaAs
MESFET Oscillator Using Large-Signal S-Parameters -Y. Mitsui ; M. Nakatani
; S. Mitsui

 A design method of
GaAs MESFET oscillator using large-signal S-parameters has been discussed.
Together with the measurement results of  the dependence of Iarge-signall S- parameters
on power levels and bias conditions, computer analysis of the equivalent
circuit for MESFET’S has qualitatively clarified the large signal properties of
MESFET’S. On the basis of these findings, S-parameters have been designed for
the MESFET oscillator over the frequency range of 6-10 GHz, which has resulted
in power

the dependence of Iarge-signall S- parameters on power
levels and bias conditions, computer analysis of the equivalent circuit for
MESFET’S has qualitatively clarified the large signal properties of MESFET’S.
On the basis of these findings, S-parameters have been designed for the MESFET
oscillator over the frequency range of 6-10 GHz, which has resulted in power
output of 45 mW at 10 GHz with 19-percent efficiency, and 350 mW at 6.5

 GHz with
26-percent efficiency, respectively. Good agreements between predicted and
obtained performances of MIC positive feedback oscillator have been
ascertained, verifying the validity of the design method using large-signal
S-parameters3.

 

(E)Temperature
Stabilization of GaAs MESFET Oscillators Using Dielectric Resonators

 C. Tsironis ; V.
Pauker

 A simple model of
the temperature stabilization of dielectric resonator FET oscillators (DRO’s)
is presented. Deduced from the oscillation condition, the model furnishes
relations for oscillation power and frequency stability with temperature. A
stack resonator with an appropriate linear resonance frequency/temperature
characteristic

 

                                 PROPOSED SYSTEM

 

-Device Structure and its Operation:

 

Fig.
1: Circuit diagram of Mesfet Oscillator

Rg- gate series resistance,

Ri- channel resistance between source and gate,

R- source series resistance,

L- common source lead inductance,

 c -g drain gate capacitance,

Cg-gate source capacitance,

 g- transconductance.

The figure below shows
a diagram of gallium arsenide (GaAs) MESFET (metal-semiconductor field-effect
transistor). MESFET is nothing but a JFET fabricated in GaAs which employs a
metal-semiconductor gate region (a Schottky diode). The device operates in
essentially the same way as does a junction-gate FET, except that instead of a
gate-channel on junction there is a gate-channel Schottky barrier. The
depletion region associated with this barrier will control the effective height
of the conducting channel and can thereby control the drain-to-source current
of the device.

Fig2:MESFET Structure

The width of this depletion region will increase with
increasing gate voltage so that we see again that the gate will be the control
electrode and as long as the Schottky barrier is reverse biased, the gate
current will be very small.

Electron mobility in
GaAs (8500 cm2/v-s) is much higher than that of silicon and
allows MESFET operation at frequencies higher than can be achieved with silicon
devices. The MESFET also possesses very short channel length. This results in
very short channel transit times for electrons. As a result, MESFET can operate
well into the range of 1 to 10 gigahertz (GHz). Thus, applications of MESFETs
were initially in microwave circuits for high frequency performance.

However, since 1984,
high-speed logic circuits employing MESFETs have been produced commercially.

These logic circuits
are made compatible with the high-speed bipolar logic family called
emitter-coupled logic (EGL).

Working principle:

Fig3: Data Flow model
of MESFET

FIG4:Cross sectional
view of mesfet model- Perspective
of a MESFET

 

The Metal-Semiconductor-Field-Effect-Transistor (MESFET)
consists of a conducting channel positioned between a source and drain contact
region as shown in the figure. The figure above flow from source to drain is
controlled by a Schottky metal gate. The control of the channel is obtained by
varying the depletion layer width underneath the metal contact which modulates
the thickness of the conducting channel and thereby the current between source
and drain.

Large signal measurements are made to
determine a mathematical relationship between only t hose parameters which vary
under large signal conditions. These relationships are included in the computer
program. Then, once the equivalent circuit has been computed from the small
signal Sparameter measurements, those parameters varying under large signals
are incrementally altered until large signal S parameters are obtained which
correspond to maximum oscillator output power. These values are used to
calculate embedding element values for six oscillator topologies. A coaxial
cavity FET oscillator was built and tested using the large signal design
theory, and it substantially verified the design technique. The second design
technique is based on the fact that S21 varied more than
other S parameters under large signals. By making design calculations based on
S21 reduced to the point corresponding to maximum

 oscillator power, it was possible to get
usable design information for an FET oscillator.

 

The
metal-semiconductor field-effect transistor (MESFET) is a unipolar device,
because its conduction process involves predominantly only one kind of carrier.
The MESFET offers many attractive features for applications in both analog and
digital circuits. It is particularly useful for microwave amplifications and
high-speed integrated circuits, since it can be made from semiconductors with
high electron mobilities (e.g., gallium
arsenide, whose mobility is five times that of silicon). Because the MESFET is
a unipolar device, it does not suffer from minority-carrier effects and so has
higher switching speeds and higher operating frequencies than do bipolar
transistors.

A
perspective view of a MESFET is given in It consists of a conductive channel
with two ohmic contacts, one acting as the source and the other as
the drain. The conductive channel is formed in a thin n-type layer supported by a high-resistivity
semi-insulating (nonconducting) substrate. When a positive voltage is applied to the drain with
respect to the source, electrons flow from the source to the drain. Hence, the
source serves as the origin of the carriers, and the drain serves as the sink.
The third electrode, the gate, forms a rectifying metal-semiconductor
contact with the channel. The shaded area underneath the gate electrode is
the depletion
region of the metal-semiconductor
contact. An increase or decrease of the gate voltage with respect to the source
causes the depletion region to expand or shrink; this in turn changes the
cross-sectional area available for current flow from source to drain. The
MESFET thus can be considered a voltage-controlled resistor.

FIG5:Cross sectional
view of mesfet model- current-voltage
characteristics of a MESFET

A
typical current-voltage characteristic of a MESFET, where the drain
current ID is plotted against the drain voltage VD for various gate voltages. For a given gate
voltage (e.g., VG = 0), the
drain current initially increases linearly with drain voltage, indicating that
the conductive channel acts as a constant resistor. As the drain voltage
increases, however, the cross-sectional area of the conductive channel is
reduced, causing an increase in the channel resistance. As a result, the
current increases at a slower rate and eventually saturates. At a given drain
voltage the current can be varied by varying the gate voltage. For example,
for VD = 5 V, one can increase the current from 0.6 to
0.9 mA by forward-biasing the gate to 0.5 V or one can reduce the current from
0.6 to 0.2 mA by reverse-biasing the gate to ?1.0 V.

A
device related to the MESFET is the  junction
field-effect transistor (JFET).
The JFET, however, has a p-n junction
instead of a metal-semiconductor contact for the gate electrode. The operation
of a JFET is identical to that of a MESFET.

There
are basically four different types of MESFET (or JFET), depending on the type
of conductive channel. If, at zero gate bias, a conductive n channel exists and a negative voltage has to be
applied to the gate to reduce the channel conductance, as shown in then the
device is an n-channel “normally on” MESFET. If
the channel conductance is very low at zero gate bias and a positive voltage
must be applied to the gate to form an n channel, then
the device is an n-channel “normally off” MESFET.
Similarly, p-channel normally on and p-channel normally off MESFETs are available.

To
improve the performance of the MESFET, various heterojunction field-effect
transistors (FETs) have been
developed. A heterojunction is a junction formed between two dissimilar
semiconductors, such as the binary compound GaAs and the ternary compound AlxGa1 ? xAs. Such junctions have many unique features that are
not readily available in the conventional p-n junctions
discussed previously.

Figure 3 shows a
cross section of a heterojunction FET. The heterojunction is formed between a
high-bandgap semiconductor (e.g., Al0.4Ga0.6As, with a
bandgap of 1.9 eV) and one of a lower bandgap (e.g., GaAs, with
a bandgap of 1.42 eV). By proper control of the bandgaps and the impurity
concentrations of these two materials, a conductive channel can be formed at
the interface of the two semiconductors. Because of the high conductivity in
the conductive channel, a large current can flow through it from source to
drain. When a gate voltage is applied, the conductivity of the channel will be
changed by the gate bias, which results in a change of drain current. The
current-voltage characteristics are similar to those of the MESFET shown
in  If the lower-bandgap semiconductor is a high-purity material, the
mobility in the conductive channel will be high. This in turn can give rise to
higher operating speed.

Fig6:Cross
section of a heterojunction FET having a conductive channel at the
heterojunction interface.

 

 

-MOTION OF ELECTRONS IN ENERGY BAND

Block parameter k:-

For free particles k = wave number =  expected value of momentum

For a particle bound to a periodic potential crystal momentum.

is not the actual momentum
but the momentum related to the constant of motion which incorporates the
crystal interaction.

This crystal momentum parameter k is also periodic with a

period of . The E-K diagram is therefore
the Energy versus crystal momentum characteristics of an electron in the
crystal.

Energy
Band Solution

Energy band solution indicates only the allowed energy
and momentum states but not about time evolution of electron’s position
etc.given E, k gives possible values of position of finding the electron with a
certain probability i.e, position is uncertain. If E is known exactly,
uncertainty in t is infinity, we can not find anything about the electron’s
position.Therefore for a particle motion we need wave packets constant
E wave function grouped about a peak energy.

Probability of finding the represented particle in a
given region of space = 1 for some specified time.

Center of mass of a particle moving with a velocity – classical idea.

wave packet also a mass – QM idea

Packet of traveling
wave with center frequency and center wave number k then
describes the particle motion represented by this group.

group velocity,  

E, k gives the center values of energy and crystal
momentum.

 

FLOW
CHART:

 

 

 

 

                                                                             

                          

 

 

                                                             

   

 

                               

METHODOLOGY

 

 

 We have done simulation in license Cogenda
Visual TCAD software,We are designing and simulating MESFET. We have used
different body material and compared with each other to evaluate best
performance among the designing of the other models we are also going to
implement this device in the oscillator circuit.We have so far designed the P-N
junction on visual Tcad Software for getting the proper Idea about our project
& seen the results of the same. We have seen the I-V characteristics,
channel length, changing material used of both the design model. After design
we will going to compare it with other devices such as Mosfet, Hemt which are
used in many such applications where Mesfet can be used.

  

APPLICATION

 

•      
Communication technology satellite and fibre
optic

•       Cell
phone                                                                                        

•       Used
for higher breakdown voltage 100kV                                           

•      
Used for higher thermal conductivity                                    

•       Simpler
technology than MOSFETs or HEMTs.                    

•       Military
application

•       Used
in Microwave frequencies more than 10^15ghz       

         

REFERENCES

 

1)       GaAs MESFET Large Signal Oscillator
Design- K.M. Johnson

 

2)      
Fabrication
of GaAs MESFET Ring Oscillator on MOCVD Grown GaAs/Si(100) Substrate- Toshio
Nonaka, Masahiro Akiyama, Yoshihiro Kawarada and Katsuzo Kaminishi Japanese
Journal of Applied Physics, Volume 23, Part 2, Number 12

 

3)       Low frequency noise physical analysis
for the improvement of the spectral purity of GaAs FETs oscillators- J.Graffeuil
.K.Tantrarongroj,.J.F.Sautereau

 

 

4)      
Design
of GaAs MESFET Oscillator Using Large-Signal S-Parameters- Y.
Mitsui ; M. Nakatani ; S. Mitsui

 

5)      
Temperature
Stabilization of GaAs MESFET Oscillators Using Dielectric Resonators- C.
Tsironis ; V. Pauker