Abstract:
The invention provides an improved acoustic energy generating apparatus that includes an improved backing structure. The improved backing structure employs protrusions that are not located in a uniform pattern along a forward side surface of the backing structure, to realize improved re-direction of acoustic energy towards a forward direction relative to the acoustic energy generating apparatus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This document is a U.S. non-provisional utility patent application of the continuation-in-part application type, and that is a continuation-in-part of, and claims priority and benefit to, U.S. non-provisional patent application Ser. No. 13/289,391, which was filed on Nov. 4, 2011, and entitled “Touch Fingerprint Sensor Using 1-3 Piezo Composites and Acoustic Impediography Principle”, and which claims priority and benefit to U.S. provisional utility patent application Ser. No. 61/410,236 which was filed on Nov. 4, 2010. Priority is claimed to all of the aforementioned patent applications, which are each incorporated herein by reference in their entirety. 
     This document is a continuation-in-part of, and further claims priority and benefit to, U.S. non-provisional utility patent application Ser. No. 13/098,964, which was filed on May 2, 2011, and entitled “Method for Making Integrated Circuit Device Using Copper Metallization on 1-3 PZT Composite”, and which claims priority and benefit to U.S. provisional utility patent application Ser. No. 61/329,605 which was filed on Apr. 30, 2010. Priority is claimed to all of the aforementioned patent applications, which are each incorporated herein by reference in their entirety. 
     This document is a continuation-in-part of, and further claims priority and benefit to, U.S. non-provisional utility patent application Ser. No. 13/277,021, which was filed on Oct. 19, 2011, and entitled “Electrical System, Method, and Apparatus of Fingerprint Sensor Using Acoustic Impediography”, and which claims priority and benefit to U.S. provisional utility patent application Ser. No. 61/394,569 which was filed on Oct. 19, 2010. Priority is claimed to all of the aforementioned patent applications, which are each incorporated herein by reference in their entirety. 
     REFERENCE TO APPLICATIONS INCLUDING RELATED SUBJECT MATTER 
     This document also includes subject matter relating to that of U.S. Patent Publication No: 2010/0237992, and to that of U.S. Patent Publication No: 2009/0279747, and to that of U.S. Patent Publication No: 20100239133, which issued as U.S. Pat. No. 8,508,103. All of these (3) aforementioned patent publications, are each incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Acoustic impedance sensors transmit acoustic energy and can be employed to measure human characteristics, including biometric characteristics. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention provides embodiments of a design of an acoustic impedance sensor including embodiments of a backing structure. 
     This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention can encompass other equally effective embodiments. The drawings are not necessarily to scale. The emphasis of the drawings is generally being placed upon illustrating the features of certain embodiments of the invention. 
       In the drawings, like numerals are used to indicate like parts throughout the various views. Differences between like parts may cause those parts to be indicated with different numerals. Unlike parts are indicated with different numerals. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which: 
         FIG. 1  illustrates a cross-sectional view of a first embodiment of an acoustic impedance sensing apparatus. 
         FIG. 2  illustrates a cross-sectional view of a second embodiment of an acoustic impedance sensing apparatus. 
         FIG. 3  illustrates a cross-section view parallel to the X and Z axes, of the upper surface of the backing layer structure. 
         FIG. 4  illustrates a side perspective view of an embodiment of a sensor, being an acoustic impedance sensing apparatus that is designed to sense surface characteristics of a finger that is direct physical contact with the sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a cross-sectional view an acoustic impedance sensing apparatus  100 . As shown, the apparatus  100  includes a first layer  110 , a second layer  120  and a third layer  130  of components. A first layer of components  110  includes an acoustic impedance sensor  112 , also referred to herein as a sensor  112 . The sensor  112  is disposed in between other components  114   a - 114   b  which function as a bezel, and are also referred to as bezel components  114   a - 114   b . A second layer of components  120  includes support structures  124   a - 124   b  and an air gap  122 . The air gap  122  is located adjacent and below a lower side of the sensor  112 . A third layer of components  130 , also referred to herein as a backing layer  130 , is disposed adjacent to a lower side of the air gap  122 . 
     In some embodiments, the sensor  112  is employed as a fingerprint touch sensor. In this embodiment, one or more fingers are disposed proximate to an upper surface of the sensor  112 . While in operation, the acoustic energy is directed from the sensor  110  towards soft tissue of the one or more human fingers disposed in proximity to the upper surface of the sensor  110 . 
     Ideally, the acoustic impedance sensor  110  directs all acoustic energy in a forward direction that is upward  102  and away from the acoustic impedance sensing apparatus  100 , as shown here. However, in practice, acoustic energy can be drawn away from the sensor  112  in many directions. In circumstances without an air gap  122  and without a backing layer  130  that is adjacent to and bounding the air gap  122 , a substantial portion of acoustic energy would likely be drawn away from the sensor  112 , in directions other than the forward direction  102 , where the forward direction is shown as being an upward direction along the Y axis  102  in  FIGS. 1-2 . 
     For example, in accordance with the Redwood Transient Model, with the apparatus  100  having the air gap  122  and backing layer  130  as shown in  FIG. 1 , the output amplitude of the acoustic energy that is being transmitted by the sensor  112 , in the upward (forward) direction  102 , is increased by 30%, as compared to an amplitude of acoustic energy transmitted in the upward (forward) direction without the air gap  122  and without the backing layer  130  including a backing layer component  132  of a particular structure and design. The backing layer component  132  is also referred to herein as a backing layer structure  132 , as a backing component structure  132  or simply as a backing structure  132 . 
     The backing layer structure  132  can be designed to provide mechanical support for the components of the other layers  110  and  120 . In this role, the backing layer structure  132  is also referred to herein as a stiffener. For the backing layer structure  132  to be effective towards increasing an amount of upward transmission of acoustic energy, the backing layer structure  132 , as a rearward medium relative to the upper (forward) side of the sensor  112 , should have a lower, and preferably a much lower, acoustic impedance than that of any forward medium relative to the upper (forward) surface of the sensor  112 . When the sensor  112  is designed as a fingerprint touch sensor, the forward medium would be the soft tissue of fingers disposed above and proximate to the upper surface of the sensor  112  (See  FIG. 4 ). 
     In some embodiments, the backing layer structure  132  is made from material having an acoustic impedance of about as low as 0.5 MRayl. This MRayl value is much lower than that of the pillar material and is lower than the acoustic impedance of any finger tissue that is disposed above the upper surface of the sensor  112 . Materials, such as those made from air gel and/or made from composite material including hollow glass spheres, can be employed to construct the backing layer structure  132  having such a low acoustic impedance of about 0.5 MRayl. 
     Although air has a low acoustic impedance value of just 1.2 KRayls, the air pocket  122  can collect moisture over time. Such moisture can interfere with the operation of the sensor  112 . 
       FIG. 2  illustrates a cross-sectional view of a second embodiment of an acoustic impedance sensing apparatus. As shown, the apparatus  200  includes a first layer  210 , a second layer  220  of components. Like  FIG. 1 , the first layer of components  110  includes an acoustic impedance sensor  112  and bezel components  214   a - 214   b . Unlike the  FIG. 1 , this embodiment includes two and not three layers, and lacks a second layer like that of  FIG. 1 , and as a result, does not employ an air gap. Instead, the second layer  220  is made as one solid backing component  232 . This embodiment is designed to address the moisture problems caused by employing an air gap, and is designed for providing structural support for other components in the acoustic sensing apparatus, if necessary. 
     In some embodiments, the second layer is molded and is also referred to as a molded backer  232  or molded base  232 . This backing component  232  is designed to make limited physical contact with a lower (back and rearward) side of the sensor  12 . 
     Like the third layer  130  of  FIG. 1 , the backing layer component  232  is made from a material having lower acoustic impedance, than material located forward (above) the top surface of the sensor  112 , also referred to herein as (forward material or forward medium), such as finger tissue, that is disposed above the upper and forward surface of the sensor  112  during its operation (See  FIG. 4 ). 
     Unlike the third layer  130  of  FIG. 1 , the backing layer  232  includes a pattern of distributed protrusions, which are also referred to as “bumps”, along its upper and forward surface. In accordance with the invention, this pattern of protrusions is preferably non-uniformly distributed. This pattern of protrusions is designed to reduce a loss (transfer) of acoustic energy from the sensor  112  in a rearward direction towards the backing layer component  232  of the backing layer  220 , by in part, reducing an amount of physically contacting surface area, between the lower (back and rearward) side of the sensor  112  and the upper side of the backing layer component  232 . The rearward direction being in an opposite direction relative to the forward direction. 
     Note that experimental results show that a non-uniform distribution of protrusions (bumps) reduces an amount of transfer of acoustic energy from the sensor  112  to the backing layer component  232 , relative to an amount of acoustic energy transfer that would occur via a uniform protrusion (bump) distribution pattern including a same number and size of protrusions (bumps). 
       FIG. 3  illustrates a cross-sectional view of the upper surface  342  of the backing layer  232 . As shown, this view is parallel to the X  104  and Z  106  axes. During manufacturing of the acoustic impedance sensor  112 , the upper side of the backing layer component  232  makes physical contact with, and could be pressed against the lower side of the sensor  112 . As a result, various shaped contact areas  302   a - 302   k  are created by protrusions (bumps) from the upper side of the backing layer component  232  touching the lower and rearward side of the sensor  112 . As shown, these contact areas  302   a - 302   k  are not restricted to having a particular two dimensional shape. Also note that the shape and size of both the upper surface  342  and the contact areas  302   a - 302   k  are to describe a concept, and embodiments of the invention are not limited to shape or scale of the upper surface  342 , nor to the shape, scale or number of contact areas  302   a - 302   k.    
     In some embodiments, the protrusions (bumps) are manufactured to have a consistent dimension and shape, and contact areas associated with these protrusions are more uniform with respect to their shape and size. In other embodiments, the protrusions (bumps) are not manufactured to have a consistent dimension and shape, and contact areas associated with these protrusions are less uniform with respect to their shape and size. 
     For example, these protrusions can have a shape and size distribution like that of a mountain range, for example, yielding a rough surface when touched. During manufacturing of the sensor  112 , the tops of the protrusions, which are shaped like mountains that are disposed along the upper (forward) surface of the backing structure, are bent and/or broken off when pressed against the lower side of the sensor  112 , to form contact area patterns like that shown in  FIG. 3 . 
     In accordance with the invention, the spatial distribution of these contact areas is preferably non-uniform. Also and preferably, each contact area is limited in size. In some embodiments, each contact area is less than the cross-sectional area of a pillar within the sensor  112 . 
     Within the sensor  112 , a first pillar is surrounded by spacing between the first pillar and other surrounding and adjacent pillars. For example, if a pillar has a 150 um height dimension (parallel to the Y axis  102 ), and a square cross-section formed by a first width dimension of 50 um (parallel to the X axis  104 ) and formed by a second width dimension ((parallel to the Z axis  106 ) of 50 um, then the cross-sectional area of the first pillar, that is parallel to the X-Z plane, is 50 um×50 um=2500 square um. 
     A longest line that can be drawn within this cross-sectional area would be a diagonal line (hypotenuse) drawn between opposite corners of this square cross-section. This longest line would have a length equaling the square root of ((50 um squared)+(50 um squared)), which would be equal to approximately 70.71 um. The length of this longest line is also referred to herein as the longest span or span within the cross-sectional area of the pillar. 
     A unit cell is the cross-sectional area of the pillar along the X-Z plane, as described above, plus one half of the surrounding gap (pitch) between pillars. For example, if the gap (pitch) between pillars is uniformly 72 um, then the cross-sectional area of the unit cell along the X-Z plane is equal to (50 um+72/2 um)×(50 um+72/2 um)=7396 square um. The longest span within that unit-cell cross sectional area is equal to the square root of ((70.71 um squared)+(70.71 um squared)), which equals a length of about 100 um. 
     Note that each contact area, regardless of its shape and size, also has a longest span, which is a longest line that can be drawn within the cross-sectional area of the contact area, parallel to the X-Z plane. In some embodiments, the span of most or of all contact areas, is less than or equal to that of the span of a pillar unit cell. In other embodiments, such spans are less than or equal to that of a span of a pillar cross-section. Limiting contact areas within such short spans reduces loss of acoustic energy in the rearward direction. 
     Experimental results indicate that, maximizing the difference between the acoustic impedance values of the material of the pillars and of the material of the backing structure  232 , increases reflection of acoustic energy by the backing structure, from the rearward to the forward direction. These results also indicate that minimizing individual and/or the total contact area between the backing structure  232  and the sensor  112  reduces loss of acoustic energy in the rearward direction from the sensor  112 . These experimental results also indicate that non-uniform distribution of individual contact areas between the sensor  112  and the backing structure  232  reduces the loss of acoustic energy in the rearward direction. 
     In some embodiments, pillars are made from a piezo-electric composite material which typically has an acoustic impedance value of 10 MRayl or higher. Selecting backing structure materials with a much lower MRayl value than 10 MRayl, is a way of creating an acoustic impedance difference between the sensor  112  and the backing structure  232  in order to cause reflection of acoustic energy to the forward direction and/or to reduce loss of acoustic energy in the rearward direction. 
     In accordance with the invention, materials with a higher MRayl value than that of the pillars can be selected to manufacture a backing structure  232 , however such materials, for example, tungsten having a high 100 MRayl value, yields an acoustic energy reflection co-efficient equal to about 74%, as opposed to 0.5 MRayl or less materials which are each instead expected to yield a higher reflection co-efficient than that of tungsten. 
     Hence, the reflection effect of the difference with respect to the MRayl value of the pillars and of the backing structure  232 , is expected to be generally less with higher than available 10 MRayl value backing structure material, than the reflection effect caused by that of available low MRayl value backing structure materials, especially those materials at or below 0.5 MRayl. However, there is room for improvement, where materials having even lower, for example 0.1 MRayl, would measurably improve the reflection effect with respect to the acoustic impedance difference between the pillars of the sensor  112  and the backing structure  232 . 
       FIG. 4  illustrates a side perspective view of an embodiment of a sensor  112 , being an acoustic impedance sensing apparatus that is designed to sense surface characteristics of finger tissue  450  that is direct physical contact with an upper surface of the sensor  112 . As shown, the sensor  112  includes a set of pillars  440 , which includes two individual pillars  440   a - 440   b  as shown. These pillars are also referred to as elements, vibrating elements or pixels. In this particular embodiment, the pillars are made from a piezo ceramic material, and are arranged into a two dimensional array. Each of the pillars  440  is designed to oscillate over time in response to an electrical voltage that also oscillates over time, and that is applied across the length (longest dimension) of each pillar  440 . The pillars abut interstitial filler material  442  that is also disposed inside of the two dimensional array of pillars  440 . 
     The finger tissue  450  is shown to be expanded in size to reveal a fingerprint valley  454  that is surrounded by neighboring fingerprint ridges  452   a - 452   b . The finger tissue  450  is disposed onto an upper protection layer  444  of the sensor  112  which forms an upper surface of the sensor  112  and which is disposed above the two dimensional array of pillars  440 . The oscillation characteristics of each pillar of the array of pillars  440  is measured to detect a presence of a fingerprint valley  454  or fingerprint ridge  452   a - 452   b  of the finger tissue  450  that could potentially be located directly above each oscillating pillar  440 . 
     Note that a first conductor grid, referred to as the upper conductor grid, resides within a thin volume of (thin layer) of space that is disposed above and abuts an upper side of the array of pillars  440 . A second conductor grid, referred to as a lower conductor grid, also resides within a thin volume (thin layer) of space that is disposed below and abuts a lower side of the array of pillars  440 . Both of the upper and lower conductor grid layers reside within the sensor  112  and are designed to apply a voltage across each of the pillars of the array of pillars  440  of the sensor  112 . 
     As shown, an embodiment of a backing component  432 , also referred to herein as a backing structure  432 , as described above, is disposed below and abuts the lower side of the sensor  112 . Hence, the backing component  432  is disposed below and preferably abuts the lower conductor grid, which abuts and is located below the two dimensional array of pillars  440 . Both the lower conductor grid and the array of pillars  440 , residing within the sensor  112 . 
     This written description uses examples to disclose the invention and also to enable a person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.