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Research in the Acoustics Group:
The Acoustic Group of the SU Microelectronics Program, in its broadest
definition, performs research in the field of Acoustic/Ultrasonic imaging
and non-desctructive testing.
To be more specific, two major research topics can be named which are in
the group's current agenda: (1) The design and realization of Capacitive
Micromachined Ultrasonic Transducers (CMUTs), and (2) Integrated Circuit
(IC) design for CMUT interfacing. The CMUT is a relatively new transducer
type, which became feasible after the advances in silicon micromachining
technology.
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| SEM image showing CMUT cells |
Layout of a CMUT driver IC |
The CMUT is essentially a micron-sized air-gap capacitor, which,
by electrostatic effects, is used for the generation and detection of
acoustic/ultrasonic waves. Major advantages associated with the CMUT
technology, compared to the conventional piezoelectric transducer field, is
the compatibility with IC manufacturing processes, ease of prodcution
and larger bandwidth, the latest of which is still a heated controversy
between the CMUT and Piezoelectric Transducer communities.
The design, optimization, fabrication and testing of CMUTs is a major research
interest of the Acoustics Group. The picture on the left is an SEM picture
of a CMUT section. This device has been manufactured by Ayhan Bozkurt at
Bilkent University. The picture on the right, then again, is a section
captured from an IC layout. The depicted cell is responsible for driving
a CMUT cell with a high-voltage pulse (+20 Volts on 70 Volts BIAS
voltage). AustriaMicroSystems AMS 0.35 um 50V CMOS technology has been
used in the design of the chip.
The CMUT offers great design flexibility due to the manufacturing process:
Silicon Micromachining. This made the device suitable for silicon integration
resulting in systems with higher imaging quality. One such application
is Intravascular Ultrasonic (IVUS) imaging. Here, the aim is to use a
circular CMUT array (as shown in the following figure) on the tip of a
catheter probe for getting images of a vein. This provides invaluable
information on arteriosklerosis, blood flow rates, and the imaging system
will serve as a guidance aid used in cardiac angiography operations.
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| CMUT array for forward-looking IVUS. |
The Acoustics Group is currently involved in a project on the design of a
CMUT based IVUS imaging system. Supported by TUBITAK, the project aims
the design of a complete imaging system that includes an annular CMUT array
together with necessary drive/read-out electronics. Target operation frequency
range is determined as 10-20 MHz, while the radius of the array will
be around 2 mm.
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| A sample HV-pulser output measurement. |
The IVUS project involves the design of transducer driving and signal
conditioning front-end ICs. High voltage CMOS technologies provided by
AustriaMicrosystems
(via Europractice)
are being used for the designs.
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