Generally, acoustic transducers convert received electrical signals to acoustic signals when operating in a transmit mode, and/or convert received acoustic signals to electrical signals when operating in a receive mode. The functional relationship between the electrical and acoustic signals of an acoustic transducer depends, in part, on the acoustic transducer's operating parameters, such as natural or resonant frequency, acoustic receive sensitivity, acoustic transmit output power and the like.
Acoustic transducers are manufactured pursuant to specifications that provide specific criteria for the various operating parameters. Applications relying on acoustic transducers, such as piezoelectric ultrasonic transducers and electro-mechanical system (MEMS) transducers, for example, typically require precise conformance with these criteria. Furthermore, these operating parameters are subject to change due to contamination, humidity, temperature and other environmental factors.
In the past, some acoustic devices have been manufactured with processes where the acoustic transducer element is placed in a metal, ceramic, or plastic package and a lid is bonded to the package. With these techniques, a device has to be first cut or otherwise separated from the rest of the wafer before it could be packaged. However, this is relatively costly and results in a packaged part with a relatively large size.
Some newer semiconductor packaging techniques employ wafer-level packaging techniques wherein packaging is performed while the device remains with its wafer. In this fashion, hundreds or thousands of packaged devices can be created simultaneously, and then separated by sawing or other means.
However, these wafer-level packaging techniques can have problems when applied to acoustic transducer devices. The sawing process can generate contaminant particles. The device may also be exposed to moisture and high heat in known these wafer-level packaging techniques that can affect the reliability and operating parameters of the device.
U.S. Pat. No. 6,265,246 discloses a wafer-level package and packaging method that provide a hermetic seal without high voltages or high temperatures. However, in general, a hermetically sealed package is not well-suited to an acoustic transducer where it is desired to communicate an acoustic wave or signal between the acoustic transducer and the external environment.
In a representative embodiment, a device comprises a first wafer, a second wafer, a gasket bonding the first wafer to the second wafer to define a cavity between the first wafer and the second wafer, and an acoustic transducer disposed on the first wafer and disposed within the cavity between the first wafer and the second wafer. The first wafer includes an aperture formed completely therethrough for communicating an acoustic signal between the acoustic transducer and an exterior of the device, said aperture being located directly beneath at least a portion of the acoustic transducer.
In another representative embodiment, a device comprises a first wafer, a second wafer, a gasket bonding the first wafer to the second wafer to define a cavity between the first wafer and the second wafer, and an acoustic transducer disposed on the first wafer and disposed within the cavity between the first wafer and the second wafer. The cavity includes an aperture for communicating an acoustic signal between the acoustic transducer and an exterior of the device
The example embodiments are best understood from the following detailed description when read with the accompanying figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.
In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatuses and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatuses are clearly within the scope of the present teachings.
Furthermore, as used herein, the term “acoustic” encompasses sonic, ultrasonic, and infrasonic. For example, a transmitting acoustic transducer may transmit sonic, and/or ultrasonic, and/or infrasonic waves. Also, unless otherwise noted, when a first device is said to be connected to, or coupled to, a node, signal, or second device, this encompasses cases where one or more intervening or intermediate devices may be employed to connect or couple the first device to the node, signal, or second device. However, when a first device is said to be “directly connected” or “directly coupled” to a node, signal, or second device, then it is understood that the first device is connected or coupled to the node, signal, or second device without any intervening or intermediate devices interposed therebetween.
Moreover, when used herein the context of describing a value or range of values, the terms “about” and “approximately” will be understood to encompass variations of ±10% with respect to the nominal value or range of values.
In one embodiment, first wafer 110 and/or second wafer 120 are semiconductor wafers, such as silicon or GaAs. In another embodiment, first wafer 110 and/or second wafer 120 are transparent substrates such as glass. Beneficially, however, first wafer 110 and second wafer 120 are made of the same material as each other to avoid thermal expansion mismatch problems.
Gasket 130 bonds first wafer 110 to second wafer 120 to define a cavity 115 between first wafer 110 and second wafer 120. Gasket 130 can be fabricated directly onto one of the bonded wafers 110 and 120, or can be applied during the bonding process. Gasket 130 could be made of silicon, or some other material applied to one of the wafers 110 and 120. A variety of materials could be used to bond the two wafers 110 and 120 together, including polymers (BCB, Polyimide, etc. . . . ) or different metals or metallic alloys (Au, Cu, Au—Hg alloy, etc. . . . ).
In one embodiment of acoustic transducer device 100, gasket 130 hermetically seals cavity 115 between first wafer 110 and second wafer 120.
In another embodiment, gasket 130 may have a structure which permits air flow to pass between the exterior of acoustic transducer device 100 and the cavity 115, which at the same time inhibiting or preventing contaminates from entering cavity 115 and coming in contact with acoustic transducer 140. An example of such a gasket 130 will be explained below with respect to
Some materials and techniques for fabricating the gasket 130 and bonding the first and second wafers 110 and 120 with gasket 130 can be found in U.S. Pat. No. 6,265,246, the entirety of which is incorporated by reference herein for all purposes as if fully set forth herein.
In one embodiment, acoustic transducer 140 may be a thin film piezoelectric device. In that case, acoustic transducer 140 may include a stacked structure of a membrane, a bottom electrode, a piezoelectric film, and a top electrode. The membrane can be fabricated with any material compatible with semiconductor processes such as poly-silicon, Silicon Nitride, Silicon Carbide or Boron Silicate Glass. The bottom electrode can be made of a metal compatible with semiconductor processes such as Molybdenum, Tungsten or aluminum. The piezoelectric film can be of a material such as Aluminum Nitride, Lead Zirconate Titanate (PZT), or other film compatible with semiconductor processes. The top electrode can be made of a metal compatible with semiconductor processes such as Molybdenum, Tungsten or aluminum.
In another embodiment, acoustic transducer 140 may comprise a piezoelectric crystal.
In acoustic transducer device 100, acoustic transducer 140 is disposed on first wafer 100 within cavity 115. Beneficially, first wafer 100 includes an aperture 145 formed completely therethrough for communicating an acoustic signal between acoustic transducer 140 and an exterior of acoustic transducer device 100. Beneficially, aperture 145 is located directly beneath (or above, depending upon orientation of the device) at least a portion of acoustic transducer 140. Acoustic transducer 140 may operate in a transmit mode for transmitting an acoustic wave or signal, a receive mode for receiving an acoustic wave or signal, or a transmit/receive mode for operating in a transmit mode during some time periods, and in a receive mode in other time periods.
In some embodiments, acoustic transducer device 100 may include more than one acoustic transducer 140 disposed within cavity 115. In that case, acoustic transducer device 100 may include an acoustic transducer array.
Beneficially, in some embodiments of acoustic transducer device 100, acoustic transducer 140 may communicate an acoustic signal to/from an exterior of acoustic transducer device 100 while at the same time maintaining a hermetic seal in cavity 115.
Beneficially, cavity 115 is constructed to optimize the acoustic performance of acoustic transducer(s) 140. The depth and width of cavity 115 may be optimized to enhance the sensitivity of acoustic transducer device 100; to amplify the output of acoustic transducer(s) 140 by constructively reflecting acoustic energy; to control the frequency; and/or suppress unwanted frequencies.
Also beneficially, first wafer 110 includes one or more vias 150 connecting acoustic transducer 140 and/or other electrical elements of acoustic transducer device 100 with external pads or contacts 160.
In acoustic transducer device 100, acoustic transducer 140 is disposed on first wafer 100. In some embodiments, first wafer 110 may also be referred to as a “base wafer,” while second wafer 120 is a “cap wafer.” In other embodiments, first wafer 110 may also be referred to as the “cap wafer,” while second wafer 120 is the “base wafer.” Acoustic transducer 140 may be disposed on either wafer.
Placing acoustic transducer 140 on one substrate and the electrical circuit(s) on the other substrate results in a much smaller footprint for acoustic transducer device 300 compared to fabricating the transducer and electrical circuit(s) separately and placing them next to each other on a printed circuit board.
By means of first and second acoustic transducers 140 and 440, acoustic energy can be transmitted (or received) simultaneously from both sides of microcap acoustic transducer device 400.
In contrast to microcap acoustic transducer device 100, in microcap acoustic transducer device 500 no aperture is provided in first wafer 110 beneath acoustic transducer 140. Nevertheless, acoustic transducer 140 may communicate an acoustic signal or wave with an exterior of microcap acoustic transducer device 500 by means of aperture 525, and/or an aperture in gasket 130 as will be described in greater detail below with respect to
Although shown in
Beneficially, microcap acoustic transducer device 500 includes an acoustic material 510 provided (e.g., as a coating) on one or more interior walls of cavity 515. Acoustic material 510 could be either reflective, or absorbing to acoustic energy, depending on the location of the material and the desired function.
Acoustic reflector(s) 610 direct acoustic energy from (or to) acoustic transducer 140 to (or from) cavity aperture 525 as shown in
Although the embodiments of
Screen 710 may comprise a foam or solid acoustically transparent solid material to allow acoustic signals to enter or exit cavity 515, but limiting the amount of debris, contaminates and moisture that can enter cavity 515. In one embodiment, screen 710 is fabricated directly in second wafer 120. In another embodiment, screen 710 is applied after bonding first and second wafers 110 and 120.
While example embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. For example, it is understood that features shown individually