Low Frequency CMUT with Vent Holes
a low frequency cmut and vent hole technology, applied in mechanical vibration separation, medical science, diagnostics, etc., can solve the problems of difficult to form a post oxide structure with a thickness that exceeds approximately 5 m (or heights that exceed 2.5 m), interfere with the quality of the resultant image,
Active Publication Date: 2013-06-06
TEXAS INSTR INC
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Benefits of technology
The present invention relates to a low frequency CMUT with vent holes. The invention aims to improve the quality of ultrasonic images by reducing interference from backward ultrasonic waves that can resonate within the semiconductor substrate. The invention includes a CMUT that has a vacuum-sealed cavity with a conductive structure that vibrates to transmit ultrasonic waves and an acoustic dampening structure that absorbs and dampens the ultrasonic waves in the substrate. The invention also includes a method for reducing interference from backward ultrasonic waves that can interfere with image quality.
Problems solved by technology
These backward ultrasonic waves can resonate within semiconductor substrate 110 depending on the thickness of semiconductor substrate 110 and the frequency of operation, and can interfere with the quality of the resultant image.
These frequencies are suitable for contact or near contact body imaging applications, like echo cardiograms, but are not suitable for airborne ultrasound applications where, for example, the object to be detected, such as the hand motions of a person playing a game, is one or more meters away.
However, forming a post oxide structure with a thickness that exceeds approximately 5 μm (or heights that exceed 2.5 μm) is difficult to accomplish because the rate of oxide growth slows dramatically when the thickness of the post oxide structure approaches 5 μm.
As a result, it is difficult to scale up CMUT 364 to accommodate these lower frequencies.
Method used
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[0038]FIGS. 4A-4B show views that illustrate an example of a CMUT 400 in accordance with the present invention. FIG. 4A shows a plan view of CMUT 400, while FIG. 4B shows a cross-sectional view taken along line 4B-4B of FIG. 4A. As described in greater detail below, CMUT 400 utilizes vent holes that allow CMUT 400 to receive and transmit low frequency ultrasonic waves.
[0039]As shown in FIGS. 4A-4B, CMUT 400 includes a semiconductor substrate 410 that has a bottom surface 412 and a top surface 414, where the top surface 414 lies in a plane 415. Semiconductor substrate 410, which is conductive, can be implemented with, for example, single-crystal silicon.
[0040]In addition, semiconductor substrate 410 has a number of vent holes 416 that extend down from the top surface 412 into semiconductor substrate 410. Further, in the FIGS. 4A-4B example, semiconductor substrate 410 has a backside opening 418 that extends up from the bottom surface 414 into semiconductor substrate 410 to expose and...
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A capacitive micromachined ultrasonic transducer (CMUT), which has a conductive structure that can vibrate over a cavity, has a number of vent holes that are formed in the bottom surface of the cavity. The vent holes eliminate the deflection of the CMUT membrane due to atmospheric pressure which, in turn, allows the CMUT to receive and transmit low frequency ultrasonic waves.
Description
BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to CMUTS and, more particularly, to a low frequency CMUT with vent holes.[0003]2. Description of the Related Art[0004]A capacitive micromachined ultrasonic transducer (CMUT) is a semiconductor-based ultrasonic transducer that utilizes a change in capacitance to convert received ultrasonic waves into an electrical signal, and to convert an alternating electrical signal into transmitted ultrasonic waves.[0005]FIGS. 1A-1B show views that illustrate an example of a prior-art CMUT 100. FIG. 1A shows a plan view of CMUT 100, while FIG. 1B shows a cross-sectional view taken along line 1B-1B of FIG. 1A. As shown in FIGS. 1A-1B, CMUT 100 includes a conventionally-formed semiconductor substrate 110, and a post oxide structure 112 that touches the top surface of semiconductor substrate 110. Post oxide structure 112, in turn, has substrate contact openings 114 that extend completely through post oxide ...
Claims
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IPC IPC(8): H01L29/84H01L21/02
CPCB06B1/0292H01L29/84H01L29/66007
Inventor ADLER, STEVENJOHNSON, PETERWYGANT, IRA OAKTREE
Owner TEXAS INSTR INC