Patent Publication Number: US-7915601-B2

Title: Electronic device including optical dispersion finger sensor and associated methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit, under 35 U.S.C. 119(e), from U.S. Provisional Application Ser. No. 60/500,475, filed Sep. 5, 2003 and U.S. Provisional Application Ser. No. 60/536,305 filed Jan. 14, 2004, the entire disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to biometric sensing, and, more particularly to biometric sensing using integrated circuit biometric sensors and associated methods. 
     BACKGROUND OF THE INVENTION 
     Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes. 
     A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,953,441 to Setlak and assigned to the assignee of the present invention. The fingerprint sensor is an integrated circuit sensor that drives the user&#39;s finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate. The patent to Setlak also discloses an approach to reduce spoofing by sensing another biometric characteristic of the user&#39;s finger, in particular, the same electric field sensing pixels are used to determine a complex impedance of the object presented to the sensor. Spoof reduction circuitry determines if the complex impedance of the presented object is indicative of a live finger. In other words, the Setlak patent discloses a biometric authentication approach that relies on multiple biometrics of the user&#39;s finger. 
     Other multi-biometric approaches may use various combinations of voice recognition, facial recognition, fingerprint recognition, and signature dynamics, for example. To satisfy the system, a user must satisfy several of the selected biometrics independently. Such systems may show enhanced selectivity over single biometric systems because false matches in one biometric characteristic are uncorrelated to false matches to a second biometric characteristic. Such a multi-biometric system may be more difficult to spoof, because each of the biometrics needs to be spoofed to compromise the system as a whole. 
     Representative of multi-biometric systems is, for example, U.S. patent application Publication No. 2002/0138768 to Murakami et al. This reference discloses sensing a heartbeat waveform that is substantially, but not necessarily completely unique, as a first biometric trait or characteristic. A second biological trait is used in conjunction with the first biological trait that is preferably also a live physiological trait. Examples of live, potentially substantially unique biological traits include the depth of the various layers of epithelial tissue from a given point on an individual&#39;s skin surface. The density of a particular kind of connective tissue, such as bone density, may be another substantially unique histological trait. Likewise, the light absorption characteristics of skin tissue or the visual retinal patterns of an iris could be substantially unique traits. Along these lines, U.S. patent application Publication No. 2003/0128867 to Bennett and U.S. Pat. No. 6,483,929 to Murakami et al. both disclose a biometric system that injects infrared energy into the user&#39;s finger and senses resulting infrared energy from the user&#39;s finger, such as to obtain the user&#39;s heartbeat as a biometric. 
     U.S. Pat. No. 6,327,376 to Harkin discloses a multi-biometric sensor including capacitive sensing pixels below a glass transparent sensing surface for sensing the ridge pattern of the user&#39;s finger. The sensor may also include an additional sensor of the contactless kind which relies for its sensing on the use of light, such as visible or infrared light, that can be positioned behind the capacitive fingerprint sensing array. 
     U.S. Pat. No. 6,560,352 to Rowe et al. discloses a biometric analysis based on using near-ultraviolet, visible, very near-infrared, or near-infrared energy and combinations thereof. U.S. Pat. No. 5,351,303 to Willmore discloses a biometric system that senses and compares the infrared image pattern from an individual&#39;s finger to another infrared image pattern of the same finger stored within system memory. Other biometric sensing approaches are also disclosed using ultrasonic imaging, such as U.S. Pat. No. 5,689,576 to Schneider et al. and U.S. Pat. No. 5,737,439 to Lapsley et al., for example. 
     Unfortunately, the prior art multi-biometric systems may have significant drawbacks. Those having two different sensors are relatively complicated, and expensive to install and operate. Those that require multiple presentations of a user&#39;s body part, for example, are inconvenient. The requirement for multiple steps also slows the process. Independent sensors may also be spoofed independently. Of course, there is a continuing need to also further develop even single biometric sensors and systems. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing background, it is therefore an object of the present invention to provide an electronic device including a compact, accurate and efficient biometric finger sensor and associated methods. 
     These and other objects, features and advantages in accordance with the present invention are provided by an electronic device including a portable housing, an optical source carried by the portable housing, and an optical dispersion finger sensor carried by the portable housing. The optical dispersion finger sensor may comprise an integrated circuit substrate adjacent the optical source so that light propagates into and is dispersed by the user&#39;s finger with at least a portion of the dispersed light exiting the user&#39;s finger in a direction toward the integrated circuit substrate. The optical dispersion finger sensor may also include at least one optical dispersion sensing pixel on the integrated circuit substrate for sensing dispersed light from the user&#39;s finger to generate optical dispersion biometric data from the user&#39;s finger. A processor may be connected to the one or more optical dispersion sensing pixels for enabling at least one device function based upon the optical dispersion biometric data. The optical dispersion biometric data may be accurately and efficiently obtained using a compact integrated circuit-based sensor. 
     The optical source may comprise an optical generator, and an optical guide having an input connected to the optical generator, and a first output exposed on the portable housing adjacent the optical dispersion finger sensor. The optical guide may also have a second output, and at least one user input key carried by the portable housing may be lighted by the second output of the optical guide. A power supply may also be carried by the portable housing and connected to the optical source. In other words, the optical source could be shared with and powered by the power supply of the electronic device for additional synergy. 
     The optical dispersion biometric data may comprise light intensity data along at least one dimension of the user&#39;s finger, for example. The optical dispersion biometric data may comprise subdermal structure data for the user&#39;s finger. In addition, the processor may further comprise a matcher for determining a match between the optical dispersion biometric data of the user&#39;s finger and stored optical dispersion biometric data for an enrolled user. 
     The optical source may comprise a broadband optical source operating over a broadband frequency range. Accordingly, the at least one optical dispersion sensing pixel may comprise optical dispersion sensing pixels having different frequency sensitivities within the broadband frequency range. For example, the optical dispersion sensing pixels may comprise buried optical detectors being buried at different depths to provide different frequency sensitivities. 
     The processor may generate the optical dispersion biometric data based upon static placement of the user&#39;s finger adjacent the integrated circuit substrate. In other embodiments, the processor may generate the optical dispersion biometric data based upon sliding placement of the user&#39;s finger adjacent the integrated circuit substrate. 
     The optical source may comprise at least one light emitting diode. The integrated circuit substrate may comprise silicon, or thin film substrate material, for example. 
     A method aspect of the invention is directed to enabling at least one function of an electronic device comprising a portable housing, an optical source carried by the portable housing, and a processor carried by the portable housing. The method may include using an optical dispersion finger sensor carried by the portable housing as described above and enabling at least one device function based upon the optical dispersion biometric data from the user&#39;s finger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a first embodiment of an electronic device including an optical dispersion finger sensor in accordance with the present invention. 
         FIG. 2  is a schematic diagram of a second embodiment of an electronic device including an optical dispersion finger sensor in accordance with the present invention. 
         FIG. 3  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 1 . 
         FIG. 4  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 2 . 
         FIG. 5  is a greatly enlarged, schematic cross-sectional view of a variation of a portion of the infrared sensor as shown in  FIG. 2 . 
         FIG. 6  is a schematic top plan view of the optical dispersion sensor as shown in  FIG. 2 . 
         FIG. 7  is a schematic diagram of a first embodiment of an electronic device including an infrared finger sensor in accordance with the present invention. 
         FIG. 8  is a schematic diagram of a second embodiment of an electronic device including an infrared finger sensor in accordance with the present invention. 
         FIG. 9  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 7 . 
         FIG. 10  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 8 . 
         FIG. 11  is a schematic plan view of an infrared sensing pixel for the infrared sensor as shown in  FIG. 7 . 
         FIG. 12  is a schematic cross-sectional view of an individual infrared antenna and thermocouple temperature sensor for the infrared sensing pixel as shown in  FIG. 11 . 
         FIG. 13  is a top plan view of the infrared antenna element and thermocouple sensor as shown in  FIG. 12 . 
         FIG. 14  is a schematic cross-sectional view of an alternate embodiment of an individual infrared antenna and thermocouple temperature sensor for the infrared sensing pixel as shown in  FIG. 11 . 
         FIG. 15  is an enlarged schematic cross-sectional view through the middle of an individual infrared antenna and temperature sensor as shown in  FIG. 12 . 
         FIG. 16  is a top plan view of an individual infrared sensing pixel as may be used in the infrared sensor as shown in  FIG. 7 . 
         FIG. 17  is an enlarged top plan view from the center portion of  FIG. 16 . 
         FIG. 18  is a schematic diagram of a first embodiment of an electronic device including a multi-biometric finger sensor in accordance with the present invention. 
         FIG. 19  is a schematic diagram of a second embodiment of an electronic device including a multi-biometric finger sensor in accordance with the present invention. 
         FIG. 20  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 18 . 
         FIG. 21  is a more detailed schematic diagram, partially in section, of a portion of the electronic device as shown in  FIG. 19 . 
         FIG. 22  is a schematic perspective view, partially in section, of an electric field finger sensing pixel as may be used in the multi-biometric finger sensor as shown in  FIG. 18 . 
         FIG. 23  is a schematic top plan view of a portion of a multi-biometric sensor embodiment including electric field sensing pixels and optical dispersion sensing pixels in accordance with the invention. 
         FIG. 24  is a schematic top plan view of a portion of another embodiment of a multi-biometric sensor including electric field sensing pixels and optical dispersion sensing pixels in accordance with the invention. 
         FIG. 25  is a schematic diagram of a multi-biometric sensor as may be used in the device of  FIG. 19  illustrating processing of biometric data therefrom. 
         FIGS. 26-28  are graphs of collected and processed optical dispersion data from three different users as may be obtained using the biometric sensor of  FIG. 19 . 
         FIG. 29  is a top plan view of a portion of yet another embodiment of a multi-biometric sensor including electric field sensing pixels and infrared sensing pixels in accordance with the invention. 
         FIG. 30  is a schematic block diagram of another embodiment of a multi-biometric sensor in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternate embodiments. 
     Referring initially to  FIGS. 1-6 , optical dispersion finger sensing as a biometric characteristic is first described. With particular reference to  FIGS. 1 and 3 , the electronic device is in the exemplary form of a cellular telephone  50  that includes a portable housing  51 . The portable housing  51  carries an optical dispersion finger sensor  55 , and a lighted keypad  52  that, in turn, includes a plurality of user operable input keys  53 . The portable housing  51  also carries a processor  54  that is connected to the optical dispersion sensor  55  and the optical source  57 . A display  58  is illustratively carried by the upper portion of the portable housing  51  and is also connected to the processor  54 . 
     The cellular phone  50  may also include a power source, such as a rechargeable battery  62 , carried by the portable housing  51  and connected to the processor  54  and other electronic components within the housing as will be appreciated by those skilled in the art. A memory  64  is also connected to the processor  54 . The optical source  57  is coupled to the keys  53  of the lighted keypad  52  by an optical guide  61  that may be a plastic body for conducting light therethrough. The optical source  57  may be an LED or electroluminescent source, for example. 
     Considered in other terms, the optical guide  61  may have an input  61   a  coupled to the optical source  57  and a first output  61   b  exposed through an opening in the housing  51 . A second output  61   c  is illustratively coupled to the keys  53  as will be appreciated by those skilled in the art. The use of the onboard optical source  57  and the minor modification to the optical guide  61  provides a relatively inexpensive approach to couple light into the user&#39;s finger  70  for optical dispersion sensing. 
     Of course, in other embodiments a dedicated optical source may be carried by the portable housing  51 . Such a dedicated optical source would permit independent control from the lighted keypad  52 , for example. 
     The optical dispersion sensor  55  includes an integrated circuit substrate  72  and a plurality of optical dispersion sensing pixels  73  on the integrated circuit substrate for sensing dispersed light from the user&#39;s finger  70 . In other embodiments, as few as one optical dispersion sensing pixel  73  may be used. More particularly, the optical source provided by the exposed optical guide output  61   b  directs light into a user&#39;s finger  70  when positioned adjacent the integrated circuit substrate  72 . The light propagates into and is dispersed by the internal tissue of the user&#39;s finger  70  so that at least a portion of the dispersed light exits the user&#39;s finger in a direction toward integrated circuit substrate  72 . This dispersed light is captured by the optical sensing pixels  73 . 
     The processor  54  is connected to the optical dispersion sensing pixels  73  for generating optical dispersion biometric data based upon dispersed light from the user&#39;s finger  70 . As will be discussed in greater detail below, the optical dispersion biometric data may comprise light intensity data along at least one dimension of the user&#39;s finger  70 , for example. The optical dispersion biometric data may additionally or alternately comprise subdermal structure data for the user&#39;s finger. 
     In addition, the processor  54  further illustratively includes a matcher  74  for determining a match between the optical dispersion biometric data of the user&#39;s finger and stored optical dispersion biometric data for an enrolled user. This match determination, in turn, may be used by a function enabler  75  of the processor to enable at least one device function, such as permitting operation of the transmit and receive functions of the cellular telephone  50 , for example. The matcher  74  and enabler  75  may be implemented on a CPU of the processor  54  operating under stored program control, as will be appreciated by those skilled in the art without requiring further discussion herein. 
     Those of skill in the art will appreciate other device functions that may be controlled, such as access to data if the electronic device were a Personal Digital Assistant (PDA), for example. Of course, many other electronic devices may benefit from the optical dispersion finger sensing, and these devices may include other access limited functions. The optical dispersion biometric data may be accurately and efficiently obtained using the compact integrated circuit-based sensor  55 . 
     Another aspect of the optical dispersion sensor  55  is that its processing may be self-contained on the integrated circuit  72  itself, or, as shown in the illustrated embodiment, the integrated circuit may contain some of the processing circuitry  77 . For example, pixel reading amplifiers and/or other image processing active devices may be provided on the substrate  72  using conventional CMOS technology. In yet other embodiments, all or a majority of the signal processing circuitry may be located off-chip. The integrated circuit substrate  72  may comprise a single crystal silicon substrate in some embodiments, or a thin film technology, such as a glass substrate, for example, in other embodiments as will be appreciated by those skilled in the art. 
     The illustrated embodiment of the optical dispersion sensor  55  is a static placement sensor. In other words, the size of the array of pixels  73  is relatively large compared to a sliding placement sensor as discussed below. Also, for the static placement sensor  55 , the processor  54  generates the optical dispersion biometric data based upon static placement of the user&#39;s finger adjacent the integrated circuit substrate  72 . 
     Referring now more particularly to  FIGS. 2 , and  4 - 6  another class of embodiments of optical dispersion finger sensor  55 ′ is now described. In these embodiments, the optical source is in the form of one or more LED optical sources  80  on the integrated circuit substrate  72 ′ itself. The illustrated optical sensor  55 ′ is also in the form of a sliding placement sensor that has a smaller sensing area over which the user slides his finger  70 ′ as will be appreciated by those skilled in the art. In these embodiments, the processor  54 ′ may collect frames of optical dispersion data from the optical dispersion sensing pixels  73 ′. In other embodiments, the LED optical sources  80  could also be used on the static placement sensor  55  described above. 
     Referring more specifically to  FIG. 5 , the plurality of optical dispersion sensing pixels may comprise optical dispersion sensing pixels  73   a ′,  73   b ′ having different frequency sensitivities f 1 , f 2  within a broadband frequency range of the light from the LED  80  or optical source  57  ( FIG. 3 ). For example, as shown in the illustrated embodiment, the optical dispersion sensing pixels may comprise buried optical detectors in the form of P/N junction detectors  73   a ′,  73   b ′ being buried at different depths to provide different frequency sensitivities. In other words, the height of the semiconductive material above a buried P/N sensing junction  73   a ′,  73   b ′ can act as a filter for different frequencies. Other filtering or frequency selection techniques are also contemplated including filter coatings, for example. More than two frequencies can also be selected by extension of these disclosed techniques as will be appreciated by those skilled in the art. 
     Those other elements of the second embodiment of the cellular telephone  50 ′ are similar to those of the first embodiment of the cellular telephone  50  described above, and are indicated with prime notation. Accordingly, these elements require no further discussion herein. 
     Referring again to  FIGS. 1-6 , a method aspect is directed to optical dispersion finger sensing. The method may comprise receiving a user&#39;s finger  70 ,  70 ′ adjacent an integrated circuit substrate  72 ,  72 ′, and directing light from an optical source  57 ,  80  into a user&#39;s finger when positioned adjacent the integrated circuit substrate. The light may propagate into and be dispersed by the user&#39;s finger  70 ,  70 ′ so that at least a portion of the dispersed light exits the user&#39;s finger in a direction toward the integrated circuit substrate  72 ,  72 ′. The method may also include sensing dispersed light from the user&#39;s finger using a plurality of optical dispersion sensing pixels  73 ,  73 ′ on the integrated circuit substrate  72 ,  72 ′, and generating optical dispersion biometric data based upon dispersed light from the user&#39;s finger  70 ,  70 ′. The method may also include enabling at least one device function based upon the optical dispersion biometric data from the user&#39;s finger  70 ,  70 ′. 
     As will be appreciated by those skilled in the art, the same set of optical dispersion sensing pixels  73 ,  73 ′ may also be used for pulse/oximetry measurements. This may be done by extracting the cardiac pulse waveform and detecting minute changes in the red to infrared intensity ratio caused by the periodic arrival of freshly oxygenated blood. 
     Referring now to  FIGS. 7-10 , various embodiments of infrared sensing pixel finger sensors  85 ,  85 ′ are first described. With particular reference to  FIGS. 7 and 9 , the electronic device is in the exemplary form of a cellular telephone  80  that includes a portable housing  81 . The portable housing  81  carries an infrared finger sensor  85 , and a lighted keypad  82  that, in turn, includes a plurality of user operable input keys  83 . The portable housing  81  also carries a processor  84  that is connected to the infrared sensor  85  and the optical source  87  for lighting the keypad  82  via the optical guide  91 . A display  88  is illustratively carried by the upper portion of the portable housing  81  and is also connected to the processor  84 . 
     The cellular phone  80  may also include a power source, such as a rechargeable battery  92 , carried by the portable housing  81  and connected to the processor  84  and other electronic components within the housing as will be appreciated by those skilled in the art. A memory  94  is also connected to the processor  84 . 
     The infrared sensor  85  includes an integrated circuit substrate  102  and a plurality of infrared sensing pixels  103  on the integrated circuit substrate for sensing infrared radiation naturally emitted from subdermal features of the user&#39;s finger  100 . The processor  84  is connected to the infrared sensing pixels  83  for generating the infrared biometric data based upon naturally emitted radiation from subdermal features of the user&#39;s finger  100 . 
     The processor  84  further illustratively includes a matcher  104  for determining a match between the infrared biometric data of the user&#39;s finger and stored infrared biometric data for an enrolled user. This match determination, in turn, may be used by a function enabler  105  of the processor  84  to enable at least one device function, such as permitting operation of the transmit and receive functions of the cellular telephone  80 , for example. The matcher  104  and enabler  105  may be implemented on a CPU of the processor  84  operating under stored program control, as will be appreciated by those skilled in the art without requiring further discussion herein. 
     Those of skill in the art will appreciate other device functions that may be controlled, such as access to data if the electronic device were a PDA, for example. Of course, many other electronic devices may benefit from the infrared finger sensing, and these devices may include other access limited functions. The infrared biometric data may be accurately and efficiently obtained using the compact integrated circuit-based sensor  85 . 
     Another aspect of the infrared sensor  85  is that its processing may be self-contained on the integrated circuit substrate  102  itself, or, as shown in the illustrated embodiment, the integrated circuit may contain some of the processing circuitry  107 . For example, pixel reading amplifiers and/or other image processing active devices may be provided on the substrate  102  using conventional CMOS technology, for example. In yet other embodiments, all or a majority of the signal processing circuitry may be located off-chip. The integrated circuit substrate  102  may preferably a silicon substrate as will be appreciated by those skilled in the art. 
     The illustrated embodiment of the infrared sensor  85  is a static placement sensor. In other words, the size of the array of pixels  103  is relatively large compared to a sliding placement sensor as discussed below. Also, for the static placement sensor  105 , the processor  104  generates the infrared biometric data based upon static placement of the user&#39;s finger adjacent the integrated circuit substrate  102 . 
     Referring now more particularly to  FIGS. 8 and 10 , another class of embodiments of infrared finger sensor  85 ′ is now described. In these embodiments, the illustrated infrared sensor  85 ′ is in the form of a sliding placement sensor that has a smaller sensing area over which the user slides his finger  100 ′ as will be appreciated by those skilled in the art. In these embodiments, the processor  104 ′ may collect frames of infrared image data from the infrared sensing pixels  103 ′. 
     Those other elements of the embodiment of the cellular telephone  80 ′ shown in  FIGS. 8 and 10  are similar to those of the embodiment of the cellular telephone  80  described above with respect to  FIGS. 7 and 9 , and are indicated with prime notation. Accordingly, these elements require no further discussion herein. 
     Turning now additionally to  FIGS. 11 through 17 , other detailed aspects of exemplary infrared sensing pixels  103  are now described. As shown in  FIG. 11 , for example, the infrared sensing pixel  103  includes an array of infrared sensing units  105  connected in series and whose output is fed to an infrared sensing amplifier (not shown). Each sensing unit  105  includes an infrared antenna in the form of a bowtie dipole antenna  106  having a relative small dimension to efficiently collect infrared energy as will be appreciated by those skilled in the art. For example, for infrared radiation at a wavelength of about 7 microns, the length L of the dipole antenna  106  may be about 3.5 microns. The overall size of the infrared sensing pixel  103  may be about 50 microns on each side as is consistent with the dimensions of a typical electric field sensing pixel as will be described in greater detail below. The infrared sensing pixels  103  may be at a density of 125 pixels per inch to capture subdermal patterns, and about 250 for ridge/valley imaging. Of course, other dimensions and types of infrared antennas may also be used as will be appreciated by those skilled in the art. 
     As shown in  FIGS. 12 ,  13  and  15 , the infrared sensing unit  109  may be advantageously formed using the various metal and polycrystalline layers, separated by interlevel dielectric layers, as are commonly used in semiconductor device processing. In the illustrated embodiment, the upper metal layer is patterned to form the two dipole antenna elements  106   a ,  106   b  of the bowtie dipole antenna  106 . An interlevel dielectric layer  107  separates the dipole elements  106   a ,  106   b  from the underlying antenna ground plane  108  provided by patterning the second metal layer as will be appreciated by those skilled in the art. Another interlevel dielectric layer  111  separates the conductive antenna ground plane  108  from the circuitry patterned using the first metal layer. 
     Two conductive vias  112   a ,  112   b  carry the signal from the dipole antenna elements  106   a ,  106   b  to a temperature sensor in the form a thermocouple having a measuring junction  114  and a reference junction  115 . Polysilicon dissipative regions  117   a ,  117   b  are used to match the impedance of about 300 ohms. Tungsten via portions  120 ,  121  illustratively connect to aluminum signal lines  122 ,  123 , respectively, patterned on the first metal layer. The thermocouple junctions are defined between the polysilicon of the first poly layer and the aluminum of the first metal layer as will be appreciated by those skilled in the art. The reference junction  115  is also shown relatively close to the measuring junction  114  for clarity of explanation; however, in other advantageous embodiments, the reference junction may be spaced considerably further away from the measuring junction. As will also be understood by those of skill in the art, an upper passivation layer  125  ( FIG. 17 ) is also provided over the dipole antenna  106 . 
     The infrared unit  105  uses a thermocouple rather than a resistor, for example, to reduce power dissipation during imaging. Of course, in other embodiments, a resistor or bolometer may be used as the temperature sensor. Each infrared unit  105  may generate an output voltage of about 0.2 to 20 microvolts, for example. 
     Another embodiment of an infrared sensing unit  105 ′ is explained with reference to  FIG. 14 . In this embodiment, the dropping resistor is provided by a portion of the substrate  117 ′. The ohmic region could also be the channel of an FET allowing modulation of the power dissipated by changing the gate voltage. The conductive vias  112   a ′,  112   b ′ allow conduction of the current wave from the dipole antenna  106 ′ through to the lower layers of the integrated circuit device. In addition, a dielectric layer  124  is provided that may provide additional ESD protection as will be understood by those of skill in the art. Those other elements of the embodiment of  FIG. 14 , not specifically mentioned, are indicated by prime notation and are similar to elements described above with reference to  FIGS. 12 and 13 . 
     As shown in top plan views of  FIGS. 16 and 17 , radial strings of infrared antennas are positioned within a circular aperture  125  through the ground plane of an infrared sensing pixel  103 . The measuring junctions are positioned beneath the infrared antennas, while signal lines connect to the reference junctions that are positioned on the periphery of the overall pixel. The reference junctions are therefore obscured from the infrared radiation by the ground plane as will be appreciated by those skilled in the art. Of course, other layouts for the infrared pixels  103 ,  103 ′ are also contemplated. 
     Referring again to  FIGS. 7-17 , another method aspect of the invention directed to infrared finger sensing is now described. The method may include receiving a user&#39;s finger  100 ,  100 ′ adjacent an integrated circuit substrate  102 ,  102 ′, and sensing infrared radiation emitted from subdermal features of the user&#39;s finger  100 ,  100 ′ positioned adjacent the integrated circuit substrate by using a plurality of infrared sensing pixels  103 ,  103 ′ on the integrated circuit substrate. Each infrared sensing pixel  103 ,  103 ′ may comprise at least one temperature sensor, such as the thermocouple junctions  114 ,  115  and  114 ′,  115 ′ described above, and at least one infrared antenna  106 ,  106 ′ above and connected to the at least one temperature sensor. The method may also include generating infrared biometric data based upon infrared radiation emitted from the subdermal features of the user&#39;s finger. 
     Referring now to  FIGS. 18 through 21 , various embodiments of multi-biometric sensing pixel finger sensors  85 ,  85 ′ are first described. With particular reference to  FIGS. 18 and 20 , the electronic device is in the exemplary form of a cellular telephone  140  that includes a portable housing  141 . The portable housing  141  carries a multi-biometric finger sensor  145 , and a lighted keypad  142  that, in turn, includes a plurality of user operable input keys  143 . The portable housing  141  also carries a processor  144  that is connected to the multi-biometric sensor  145  and the optical source  147  for lighting the keypad  142  via the optical guide  151 . A display  148  is illustratively carried by the upper portion of the portable housing  141  and is also connected to the processor  144 . 
     The cellular phone  140  may also include a power source, such as a rechargeable battery  152 , carried by the portable housing  141  and connected to the processor  144  and other electronic components within the housing as will be appreciated by those skilled in the art. A memory  154  is also connected to the processor  144 . The multi-biometric sensor  145  includes an integrated circuit substrate  162 , a first set of biometric sensing pixels  103   a  on the integrated circuit substrate for sensing a first finger biometric characteristic to generate first finger biometric characteristic data having a first matching selectivity. 
     The sensor  145  also includes a second set of biometric sensing pixels  103   b  on the integrated circuit substrate  102  for sensing a second finger biometric characteristic different than the first finger biometric characteristic to generate second finger biometric characteristic data with a known spatial relationship to the first fingerprint characteristic data. The second finger biometric characteristic data may have a second matching selectivity less than the first matching selectivity. Accordingly, a lower selectivity characteristic can be combined with a higher selectivity to provide more accurate results, for example, in a compact sensor package based on integrated circuit technology. 
     The processor  144  is connected to first and second sets of sensing pixels  163   a ,  163   b  for generating the first and second biometric characteristic data. 
     The first biometric characteristic data may comprise fingerprint image data, for example. Other imaging data establishing known locations on the user&#39;s finger  160 , such as based upon minutiae patterns, could also be used, as well as other similar data establishing a known spatial relationship that may be correlated to the second biometric characteristic data. Accordingly, for these embodiments the processor  144  further illustratively includes a high/low selectivity correlator  159  for cooperating with the first and second sets of biometric sensing pixels  103   a ,  103   b  for spatially correlating the second finger biometric data relative to the fingerprint image data. To also provide a known temporal relationship between the data, the processor  144  may operate the first and second sets of biometric sensing pixels  103   a ,  103   b  substantially simultaneously. 
     A matcher  164  is connected to the correlator  169  for determining a match between the multi-biometric data of the user&#39;s finger  160  and stored multi-biometric biometric data for an enrolled user. This match determination, in turn, may be used by a function enabler  165  of the processor  144  to enable at least one device function, such as permitting operation of the transmit and receive functions of the cellular telephone  140 , for example. The correlator  169 , the matcher  164 , and enabler  165  may be implemented on a CPU of the processor operating under stored program control, as will be appreciated by those skilled in the art without requiring further discussion herein. 
     Those of skill in the art will appreciate other device functions that may be controlled, such as access to data if the electronic device were a PDA, for example. Of course, many other electronic devices may benefit from the multi-biometric finger sensing, and these devices may include other access limited functions. The multi-biometric characteristic data may be accurately and efficiently obtained using the compact integrated circuit-based sensor  145 . 
     Another aspect of the infrared sensor  85  is that its processing may be self-contained on the integrated circuit substrate  162  itself, or, as shown in the illustrated embodiment, the integrated circuit may contain some of the processing circuitry  167 . For example, pixel reading amplifiers and/or other image processing active devices may be provided on the substrate  162  using conventional CMOS technology, for example. In yet other embodiments, all or a majority of the signal processing circuitry may be located off-chip. The integrated circuit substrate  162  may preferably a silicon substrate as will be appreciated by those skilled in the art. 
     The illustrated embodiment of the multi-biometric sensor  145  is a static placement sensor. In other words, the size of the array of pixels  163   a ,  163   b  is relatively large compared to a sliding placement sensor as discussed below. Also, for the static placement sensor  145 , the processor  144  generates the multi-biometric characteristic data based upon static placement of the user&#39;s finger adjacent the integrated circuit substrate  162 . 
     Referring now more particularly to  FIGS. 19 and 21 , another class of embodiments of multi-biometric finger sensors  145 ′ is now described. In these embodiments, the illustrated multi-biometric sensor  145 ′ is in the form of a sliding placement sensor that has a smaller sensing area over which the user slides his finger  160 ′ as will be appreciated by those skilled in the art. In these embodiments, the processor  144 ′ may collect frames of infrared biometric data from the sensing pixels  103   a ′,  103   b′.    
     U.S. Pat. No. 5,351,303 to Willmore schematically discloses a contact sensor for reading the infrared profile of the finger, but no successful implementation of the method described is known to date. Such an infrared sensor may suffer from sensitivity to both conducted thermal energy and radiated thermal energy. In the finger contact application, the conducted thermal energy is generally dominant, and in it the pattern of the finger surface friction ridges dominates. The patterns of the subdermal sources, such as the arterial blood supply are overwhelmed by the strong ridge pattern signal. While reading the friction ridge pattern can be useful, that is not typically required for the infrared sensors in the multi-biometric sensor embodiments. In this case, the friction ridge pattern is noise, and the pattern of the subdermal features sources is the unique data the sensor is attempting to capture. 
     The infrared sensor arrays of the prior art may also suffer from the omni-directional sensitivity pattern of the pixels. Crosstalk between pixels may become a debilitating problem if the thermal structures to be imaged are farther away from the array than 3 or 4 times the pixel pitch. This is indeed the case when imaging the subdermal structures of the finger. To be successful, the pixels should have some form of focusing that minimizes crosstalk. 
     The infrared sensors  85 ,  85 ′ as disclosed herein may use a differential thermal sensing that rejects heat conducted through the surface of the device (that contains primarily the friction ridge pattern) and detects radiant infrared heat (which contains patterns primarily representative of the subdermal arterial blood distribution). The antenna and temperature sensor structure provides the focusing to reduce or minimize crosstalk between the pixels and develop clean image of the subdermal thermal pattern. The infrared sensors  85 ,  85 ′ can be fabricated in existing standard CMOS silicon foundry processes as will be appreciated by those skilled in the art. 
     Those other elements of the embodiment of the cellular telephone  140 ′ shown in  FIGS. 18 and 21  are similar to those of the embodiment described above with respect to  FIGS. 18 and 20 , and are indicated with prime notation. Accordingly, these elements require no further discussion herein, 
     Referring now additionally to  FIG. 22 , an embodiment of a high selectivity biometric characteristic sensing pixel  163   a  in the form of an electric field sensing pixel is now described. The electric field sensing pixel  163   a  may also be considered or referred to as an RF sensing pixel in view of its operating frequency as described below. 
     In particular, the electric field sensor pixel  163   a  includes one or more active semiconductor devices formed on the substrate  162 , such as the schematically illustrated amplifier  180 . A first metal layer  181  interconnects the active semiconductor devices. A second or ground plane electrode layer  182  is above the first metal layer  181  and separated therefrom by an insulating layer  184 . A third metal layer  185  is positioned over another dielectric layer  186 . In the illustrated embodiment, the a first external electrode  190  is connected to an excitation drive amplifier  191  which, in turn, drives the finger  160  with a signal that may be typically in the range of about 1 KHz to 1 MHz. Accordingly, the drive or excitation electronics are thus relatively uncomplicated and the overall cost of the electric field sensing pixel  163   a  may be relatively low, while the reliability is great. 
     An illustratively circularly shaped electric field sensing electrode  192  is on the insulating layer  186 . The sensing electrode  192  may be connected to sensing integrated electronics, such as the illustrated amplifier  180  formed adjacent the substrate  162  as schematically illustrated, and as would be readily appreciated by those skilled in the art. 
     An annularly shaped shield electrode  195  surrounds the sensing electrode  192  in spaced relation therefrom. As would be readily appreciated by those skilled in the art, the sensing electrode  195  and its surrounding shield electrode  195  may have other shapes, such as hexagonal, for example, to facilitate a close packed arrangement or array of sensing pixels. The shield electrode  195  is an active shield which is driven by a portion of the output of the amplifier  180  to help focus the electric field energy and, moreover, to thereby reduce the need to drive adjacent electric field sensing electrodes. 
     The electric field sensing pixel  163   a  also illustratively includes an upper passivation layer  197 , and an optional ESD electrode  196 . The electric field sensor pixel  163   a  includes only three metal or electrically conductive layers  181 ,  182  and  185 / 195 . The sensing pixels  163   a  can be made without requiring additional metal layers that would otherwise increase the manufacturing cost, and, perhaps, reduce yields. Accordingly, the overall multi-biometric sensor  145  may less expensive and may be more rugged and reliable than a sensor including four or more metal layers as would be appreciated by those skilled in the art. As will be appreciated by those skilled in the art, the construction of the electric field sensing pixels  163   a  is also fully compatible with the optical dispersion and/or infrared sensing pixels described herein. 
     The electric field sensing pixel  163   a  and various processing features and further advantages are disclosed, for example, in U.S. Pat. No. 5,953,441 to Setlak and assigned to the assignee of the present invention. The entire contents of this Setlak patent are incorporated herein by reference. The patent also discloses use of the electric field sensing pixel  163   a  to determine a complex impedance of the user&#39;s finger to thereby aid in reducing the likelihood of spoofing the sensor with other than a live finger. In the present multi-biometric sensor  145 , the electrical field sensing pixel  163   a  could also be used in complex impedance measuring as another biometric characteristic of the user to aid in efficient matching. 
     Each of the second set of biometric sensing pixels of the multi-biometric sensor  145  may comprise an optical dispersion sensing pixel  163   b  for sensing dispersed light from the user&#39;s finger, in combination with the electric field sensing pixels as shown an embodiment of  FIG. 23 . In this embodiment, the electric field drive ring  190  extends around the periphery, and the two pixel types are intermingled in the sensing area. The light source is provided by the surface emitting LED  200  carried by the integrated circuit substrate  162 . 
     Another possible layout of the optical dispersion sensing pixels  163   b ′ and electric field sensing pixels  163   a ′ is shown in  FIG. 24 . In this embodiment of a multi-biometric sensor  145 ′, the optical dispersion pixels are arranged in first and second groups flanking the array of electric field sensing pixels  163   a ′. The finger drive electrode  162 ′ is also shown as two segments on the outside of the respective first and second groups of optical dispersion sensing pixels  163   b ′. In this embodiment, the light source  200 ′ is provide from off the integrated circuit substrate  162 ′. 
     Turning now additionally to  FIG. 25 , advantageous processing of the multi-biometric data from a multi-biometric finger sensor  210  is described. The illustrated multi-biometric sensor  210  is of the slide type including electric field sensing pixels and optical dispersion pixels as described above. The optical source  212  is located on the integrated circuit substrate in the illustrated embodiment. A static placement multi-biometric sensor may produce similar data as will be appreciated by those skilled in the art. 
     In particular, a first sequence of relative intensity data is illustrated by the image blocks  213   a - 213   a - 213   d . The light intensity is sequentially sensed at two spaced points in the X-direction, that is, the direction of advancement of the user&#39;s finger  215 , the intensity at these two spaced positions is plotted in the upper and lower curves of the graph  216 . As expected, the curve from the location closer to the optical source  212  is greater than from the other spaced location. As also shown, a difference between these two curves is determined and plotted in the graph  217 . As can be seen the difference in local light dispersion seen in lower graph  217  varies with position along the finger. 
     Referring now briefly to the curves of  FIGS. 26 ,  27  and  28  for different individuals A, B and C, it can be seen that the optical dispersion data so compiled is indeed unique to the different individuals over repeated measurements. Accordingly, the optical dispersion data so processed may serve as a valuable biometric matching characteristic especially in combination with the higher selectivity provide by the fingerprint friction ridge image sensing provided by the electric field sensing pixels. 
     Returning now again to  FIG. 25 , and the right hand side thereof, a series of optical images enhanced to show ridges, valleys, pores, etc. is shown. As noted in Block  220  these enhanced images can be matched and used to establish exact locations of the frames along the finger  215 . As noted at processing Block  221  the enhanced images can also be used by classical fingerprint matching. Moreover, subdermal structures, such as pores are especially clear in optical dispersion images. 
     Referring now additionally to  FIG. 29 , another multi-biometric sensor  225  is now described. In this embodiment, infrared sensing pixels  227  on the integrated circuit substrate  232  provide the second set of biometric sensing pixels having the lower selectivity, while electric field sensing pixels  228  provide the sensing pixels having the higher matching selectivity. A drive electrode  233  is also illustratively positioned around the periphery of the sensor  225 . Of course, exemplary embodiments of infrared sensing pixels are extensively described above and need no further description here. If the operating frequencies of the different sensing pixels  227 ,  228  is sufficiently different, e.g. on the order of 10 6  Hz apart, it is likely that both types of sensing pixels can be operated simultaneously. Those of skill in the art will appreciate in that other embodiments, the selectivity of the electric field sensing pixels  228  could be less than the infrared sensing pixels  227 , such as by altering the relative numbers of each, for example. 
     With additional reference to  FIG. 30 , another multi-biometric sensing and matching system  235  is now explained. In this embodiment, a number of the above-described biometric finger characteristic sensing and processing aspects are combined. The system  235  illustratively includes a multi-biometric sensor  236  coupled to a multi-biometric matcher  237 . The multi-biometric sensor  236  includes an integrated circuit substrate  240  upon which electric field sensing pixels  241 , optical dispersion sensing pixels  242 , and infrared sensing pixels  243  are provided. 
     A processor executing a respective software module performs complex skin impedance measuring using the electric field sensing pixels  241  at Block  245 . The electric field sensing pixels  241  are also operated to generate a friction ridge pattern by Block  246 . Similarly, Block  247  produces an optical dispersion skin pattern from the optical dispersion sensing pixels  242 . In addition, the infrared sensing pixels are used to generate subdermal thermal or infrared patterns by Block  250 . The data produced by Blocks  245 ,  246 ,  247  and  250  is illustratively fed to Block  251  for signal processing and data conversion. 
     The outputs of the signal processing and data conversion Block  251  are coupled to several modules or Blocks in the multi-biometric matcher  237 . In particular, the finger impedance matcher of Block  255  receives an output, as do the finger pattern matcher of Block  256 , the finger optical dispersion pattern matcher of Block  260 , and the thermal pattern matcher of Block  257 . As explained above, it may be desirable to spatially correlate the thermal or infrared pattern data and optical dispersion data to a finger location and this is done by coupling outputs of the fingerprint pattern matcher of Block  256  to Blocks  257  and  260 . 
     Lastly as shown in the illustrated system  235  Block  261  may be used to perform a statistical match decision. This may be done by a simple voting algorithm or by more sophisticated weighting algorithms as will be appreciated by those skilled in the art. 
     The types of multi-biometric sensors disclosed herein, containing a mixture of different sensor types has several advantages over both traditional single biometric sensors, and over non-integrated sets of multi-biometric measurements. Multiple biometrics methods can be satisfied simultaneously and in the same small physical space. The temporal and spatial simultaneity requirement makes spoofing more difficult. The sensors are easy and convenient use, as the user can provide a single presentation of a single body part, such as the finger, while generating multiple biometric measurements for use in high accuracy identification and identity verification, greatly simplifying and speeding up multi-biometric measurements. The sensors provide a single acquisition/signal-processing device that integrates the measurement of several different biometric characteristics, eliminating the need for multiple independent reading devices and signal processing systems, and eliminating the excessive equipment cost of prior art multi-biometric systems. 
     An advantage of the multi-biometric sensor embodiments disclosed herein is that they can use biometric measurements that, by themselves, have only a limited degree of selectivity between people. These low-selectivity biometrics have rarely been exploited in the past because by themselves they are not very useful. A combination of several of these biometrics, however, if they are statistically orthogonal and acquired simultaneously, can have a joint selectivity that approaches the mathematical product of the individual selectivities. Less selective biometrics can be combined with stronger biometrics, such as fingerprint verification, to yield a system with very strong selectivity that is much more difficult to spoof than the single high-selectivity biometric alone, such as the fingerprint alone. 
     Some of the secondary biometrics, such as finger thermal profile, generate very diffuse image characteristics. Since there are no definite edges in the images, it is difficult find the proper alignment for matching. When an image of the same area is taken simultaneously using both a strongly edged characteristics, e.g. the fingerprint, and a diffuse characteristic, e.g. the finger thermal profile, the exact alignment of the match data with the template can be established using the edged characteristic. This alignment can then be applied to the diffuse characteristic, permitting a higher confidence match assessment of that characteristic. The result is a small, inexpensive, easy to use multi-biometric sensor that has performance exceeding that of the traditional biometric systems, both in terms of match accuracy and spoof reduction. 
     The multi-biometric sensors described herein are envisioned as fabricated on a silicon integrated circuit substrate, with the various sensors and signal processing integrated into the silicon. The user places his finger on the device, and the system reads several different properties or biometric characteristics of the finger skin adjacent to the sensor simultaneously. Examples of the kind of biometric measurements and sensors that could be used include any of the various kinds of sensing mechanisms known to measure the physical friction ridge structure of the skin. Such sensors include optical systems, RF imaging systems, contact temperature and thermal flux systems, electrical capacitance systems, pressure measuring systems, vibration damping systems, ultrasonic systems, etc. Also possible are electronic mechanisms for detecting the bulk electrical and electromagnetic properties of the skin, such as electrical impedance sensors. In addition, sensing mechanisms for detecting the optical transmission of dispersion properties of the skin such as photo-detectors, photo-emitters, filters, gratings, coatings, etc. may be used in yet other embodiments. 
     Devices that measure the subdermal thermal profile of the finger such as Infrared cameras, and infrared sensor arrays could also be used. Sensors that detect properties of the blood, cardiac pulse, or other inner structures of the skin, such as pulse-oximetry detectors, deep reading optical or infrared emitters and detectors, pulse pressure sensors etc. may be used in other embodiments. In addition, sensors can be used that measure the bulk mechanical stiffness or low frequency mechanical damping properties of the skin, such as force gages or stain gages, pressure sensing elements, vibrating elements, accelerometers, etc. Other sensors that measure properties of the layered structures of the skin, such as ultrasonic transducers, may be used. Devices that measure skin surface chemistry, such as semiconductor electrolyte ion detectors, etc. may also be used in various other embodiments of the multi-biometric sensors described herein as will be appreciated by those skilled in the art. 
     Other related features and aspects of the sensors described herein may be found in copending patent applications entitled FINGER SENSOR USING OPTICAL DISPERSION SENSING AND ASSOCIATED METHODS, Application Ser. No. 10/935,482; MULTI-BIOMETRIC FINGER SENSOR INCLUDING OPTICAL DISPERSION SENSING PIXELS AND ASSOCIATED METHODS, Application Ser. No. 10/935,705; MULTI-BIOMETRIC FINGER SENSOR INCLUDING ELECTRIC FIELD SENSING PIXELS AND ASSOCIATED METHODS, Application Ser. No. 10/935,703; MULTI-BIOMETRIC FINGER SENSOR USING DIFFERENT BIOMETRICS HAVING DIFFERENT SELECTIVITIES AND ASSOCIATED METHODS, Application Ser. No. 10/935,704; INFRARED BIOMETRIC FINGER SENSOR INCLUDING INFRARED ANTENNAS AND ASSOCIATED METHODS, Application Ser. No. 10/935,484; INFRARED BIOMETRIC FINGER SENSOR AND ASSOCIATED METHODS, Application Ser. No. 10/935,468; and MULTI-BIOMETRIC FINGER SENSOR INCLUDING INFRARED SENSING PIXELS AND ASSOCIATED METHODS, Application Ser. No. 10/935,483, assigned to the assignee of the present invention and the entire subject matter of which is incorporated herein by reference. Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.