Brief description on surface acoustic and bulk acoustic wave devices

1. SURFACE AND BULK
ACOUSTIC DEVICES
BY
JENY JOSE
PRK18PH1005

2. CONTENTS
• INTRODUCTION
• SURFACE ACOUSTIC WAVE
• SCHEMATIC REPERSENTATION
• BULK ACOUSTIC WAVE DEVICE
• CHARACTERISTICS OF ELECTRODES AND PIEZO
ELECTRIC MATERIALS
• COMPARISON BETWEEN SAW AND BAW DEVICE
• APPLICATION
• CONCLUSION
• REFERANCE

3. INTRODUCTION
• In a crystalline solid a sound wave is
transmitted as a result of the displacement of
the lattice point about their mean position.
• Surface acoustic waves propagate along the
surface of the substrate.
• Bulk acoustic waves propagate through the
bulk substrate materials .

4. SURFACE ACOUSTIC WAVES
• A surface acoustic wave (SAW) is an acoustic
wave traveling along the surface of a material
exhibiting elasticity, with an amplitude that
typically decays exponentially with depth into
the material.
• Acoustic waves (also known as sound waves)
are a type of longitudinal waves that
propagate by means of adiabatic compression
and decompression.

5. • SAWs were first explained in 1885 by Lord
Rayleigh thus waves are named as Rayleigh
waves
• Rayleigh waves have a longitudinal and a
vertical shear component that can couple with
any media in contact with the surface. This
coupling strongly affects the amplitude and
velocity of the wave, allowing SAW sensors to
directly sense mass and mechanical
properties.

6. Schematic picture of SAW device

7. • The velocity of acoustic waves is typically
3000m/s, which is much lower than the velocity
of the electromagnetic waves.
• SAW devices use SAWs in electronic components
to provide a number of different functions,
including delay line(Propagation delay, the length
of time taken for something to reach its
destination ) filters, correlators and AC to DC
converters.
• SAW filters are now used in mobiles and provide
significant advantages in performance, cost, and
size over other filter technologies such as quartz
crystals (based on bulk waves), LC filters, and
waveguide filters.

9. BULK ACOUSTIC WAVE DEVICES
• BAW resonator is like a simple capacitor. An
acoustic wave could be generated when a
differential voltage is applied on two
electrodes, and it will produce acoustic
reflection to the surfaces. In this case, the
resonance is produced by the excitation of
wave to the thickness direction and
determined by the properties of piezoelectric
film and electrodes

11. CHARACTERISTICS OF ELECTODES
AND PIEZOELECTRIC MATERIAL
To achieve enough acoustic reflection between two
metallic electrodes, the choices of both electrode materials
and piezoelectric materials must be well considered.
Aluminum (Al) owns good electrical conductivity but low
acoustic impedance; Tungsten (W) and Molybdenum (Mo)
present high acoustic impedances but very disappointed
conductivity. In such case, combining Al and W to obtain
their good properties is considered to achieve the purpose
of good conductivity and high acoustic impedance in
electrode materials. On the other hand, Aluminum Nitride
(AlN) is the most common used material for the
piezoelectric film in BAW devices, because it owns the best
balance of performance, manufacturability and reliability

12. COMPARISION BETWEEN SAW
DEVICES AND BAW DEVICES
• SAW devices work at low frequency (below
1GHz). At higher frequency its power handling
capacity becomes less. They are quite sensitive to
temperature change
• Unlike SAW devices, BAW filters have the ability
of occupying good performance above 2GHz
frequency with less loss in a tiny size. In addition,
BAW devices are far less sensitive to temperature
changes even at broad bandwidths.

14. APPLICATIONS
• SAW and BAW device coverage includes delay lines and filters
operating at selected frequencies in the range from about 10
MHz to 11 GHz.
• Modeling with single-crystal piezoelectric and layered
structures; resonators and low-loss filters; comb filters and
multiplexers; antenna duplexers; harmonic devices; filters for
pulse compression.
• Filters acoustic and acoustoelectric correlators for radar, spread
spectrum, and packet radio; acousto-optic processors for Bragg
modulation and spectrum analysis.
• Real-time Fourier-transform and cestrum processors for radar
and sonar.
• Filters for microwave digital radio; clock-recovery filters for fiber
communications.

15. CONCLUSION
• The BAW devices have replaced the traditional
SAW filters to dominate the market of microwave
filters, which is mainly due to their good
performance and miniature size in the
circumstance of high frequency (over 2G). The
BAW resonators are the most critical elements of
devices, which act as a simple capacitor.
• With the development of 4G network, the
popularity of tablet computers and the
deployment of microwave devices, the
application of BAW devices will be even broad.

16. REFERENCE
• https://en.wikipedia.org/wiki/Surface_acousti
c_wave
• Zufu Chen, Master, ECS of Southampton
University” Bulk Acoustic Wave Devices”.
• C K CAMPBELL” Applications of surface
acoustic and shallow bulk acoustic wave
devices”.
• https://youtu.be/eppp7rIlQ_M