Surface micromachined ultrasonic transducer

Details Surface micromachined ultrasonic transducer Surface micromachined ultrasonic transducer

1999-04-27

2001-11-20

Wojciechowicz, Edward (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Physical deformation

C257S416000, C257S417000, C257S419000, C257S528000

Reexamination Certificate

active

06320239

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to an ultrasonic transducer and more particularly to an ultrasonic transducer that is manufactured with surface micromachining.
The publication by I. Ladabaum et al., “Micromachined Ultrasonic Transducers (MUTs)” in 1995 IEEE Ultrasonics Symposium, pages 501 through 504, descloses an ultrasonic transducer that was manufactured with the method of surface micromachining. Ultrasonic transducer emitting diaphragms were produced on a silicon substrate by etching out 1 &mgr;m thick oxide layers.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved ultrasonic transducer that can be employed for farther-reaching integration.
This object is achieved in accordance with the present invention in an ultrasonic transducer which uses the method of surface micromachining, as employed in the framework of a VLSI process, particularly a CMOS process, in order to integrate micromechanical components together with drive electronics on a chip. A thin layer, which is preferably polysilicon but, can also be silicon nitride at least in part, is used as a diaphragm of the ultrasonic transducer. This thin layer is formed on an auxiliary layer, so that a slight interspace can be created between the diaphragm and a substrate by etching out the auxiliary layer. The excitation of ultrasonic oscillations electrosatically ensues because the diaphragm is made to be electrically conductive (by doping the polysilicon or by applying a conductive layer) and an electrically conductive region is formed in the substrate by doping. Fundamentally, the electronic circuits previously utilized for ultrasonic transducers can also be employed here. However, micromachine ultrasonic transducers can advantageously be integrated on the same substrate as electronic drive components.
New application possibilities derive as a result thereof in contrast to previous, non-integrated solutions, resulting in cost-beneficial and dependable circuits. A preferred embodiment provides additional protective measures that decouple the operating circuit of the transducer from a drive or evaluation circuit such that more sensitive components are protected against over-voltages. Alternative embodiments provide additional measures with which the conductivity or stiffness of the diaphragm are adapted. The inventive transducer is especially well-suited for arrays, i.e. for grid-shaped arrangements of a number of individual transducers that can be driven individually or in groups as needed. The far-reaching integration of the inventive ultrasonic transducer makes it possible to connect such an array to electronic circuits in a comparatively simple way. As a result of the micromachine embodiment of the transducer itself, the transducer can be offered in a number of embodiments, particularly in largely miniaturized dimension. Due to the integration of the required drive and evaluation circuits on the substrate, influences of external disturbances are minimized; complicated electrical wiring is eliminated; sensor-specific signal processing on the chip is possible, which further simplifies the drive from the outside; and the transducers can be cost-beneficially manufactured in high numbers and with low manufacturing tolerances.


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“Micromachined Ultrasonic Transducers: 11.4 MHz Transmission in Air and More”, Ladabaum et al., Appl. Phys. Lett. vol. 68(1) (1996), pp. 7-9 Jan.
“A Surface Micromachined Elecrostatic Ultrasonic Air Transducer”, Haller et al., IEEE Trans. Ultrason., Ferroelect. Freq. Contr. vol. 43(1) (1996), pp. 1-6, Jan.
“Silicon Condenser Microphone with Integrated Field-Effect Transistor”, W. Kuhnel, Sensors and Actuators, vol. 26 (1991), pp. 521-525 (1991), Jan.
“Micromachined Ultrasonic Transducers (MUTs)”, Ladabaum et al., 1995 IEEE Ultrasonics Symposium (1995), pp. 501-504, Jan.

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