Patent Publication Number: US-9418273-B2

Title: Structure for multicolor biometric scanning user interface

Description:
FIELD 
     The present application relates generally to biometric scanning and, more specifically, to a structure for a multicolor biometric scanning user interface. 
     BACKGROUND 
     As mobile telephones have received increasing amounts of computing power in successive generations, the mobile telephones have been termed “smart phones.” Along with increasing amounts of computing power, such smart phones have seen increases in storage capacity and, consequently, increased utility. Beyond telephone functions, smart phones may now send and receive digital messages, be they formatted to use email standards, Short Messaging Service (SMS) standards, Instant Messaging standards and proprietary messaging systems. Smart phones may also store, read, edit and create documents, spreadsheets and presentations. Accordingly, there have been increasing demands for smart phones with enhanced privacy. Such enhanced privacy is frequently accomplished using authentication functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made, by way of example, to the accompanying drawings which show example implementations; and in which: 
         FIG. 1  illustrates an anterior side of a mobile communication device featuring a multicolor fingerprint scanning interface; 
         FIG. 2  illustrates an example arrangement of internal components of the mobile communication device of  FIG. 1 ; 
         FIG. 3  illustrates example steps in a method of changing the color of the multicolor fingerprint scanning interface to a default color matching the device of  FIG. 1 ; 
         FIG. 4  illustrates example steps in a method of changing the color of the multicolor fingerprint scanning interface responsive to a user finger approaching the device of  FIG. 1 ; 
         FIG. 5  illustrates example steps in a method of changing the color of the multicolor fingerprint scanning interface responsive to a user finger contacting the device of  FIG. 1 ; 
         FIG. 6  illustrates example steps in a method of changing the color of the multicolor fingerprint scanning interface responsive to a user finger ending contact with the device of  FIG. 1 ; and 
         FIG. 7  illustrates example steps in a method of changing the color of the multicolor fingerprint scanning interface dependent upon success of authentication. 
         FIG. 8  illustrates, in cross-section, a finger and an example fingerprint sensor; 
         FIG. 9  illustrates, in cross-section, an example structure for the multicolor fingerprint scanning interface of  FIG. 1 , the example structure including a mixed-element layer; and 
         FIG. 10  illustrates, in plan view, the mixed-element layer of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Today&#39;s smart phone unit with any type of fingerprint sensor may be perceived to have at least one flaw—sensor color. The lack of color option for surface of the fingerprint sensor may be seen to make the user experience sub-optimal and some may consider that, from an industrial design perspective, the fingerprint sensor appears out of place. Most smart phones have a housing whose top surface (plastic and screen frame) is uniformly colored, with the oft-used colors including black, white, and shades of grey. 
     The surface of the fingerprint sensor, to remain functional for most solutions, may not be painted. As such, a dark “gold” sensor color stands in contrast to the color of the remainder of the top surface of the device. The dark “gold” color is the typical natural color Complementary Metal Oxide Semiconductor (CMOS) silicon as seen through a substantially transparent protective layer. The protective layer may be, for example, epoxy or, for another example, glass. The protective layer may be, for an even further example, a combination of epoxy and glass. 
     It is proposed herein to enhance the user experience and appearance of a smart phone fingerprint sensor. 
     A mobile computing device may include a biometric sensor with a color-controlled layer positioned in proximity to the biometric sensor. The color-controlled layer may be overlaid on top of the sensor, or it may be placed underneath the sensor. Where the color of the color-controlled layer may be changed, a processor of the mobile computing device may control the color of the color-controlled layer responsive to sensing various conditions. For example, the color of the color-controlled layer may be controlled, by default, to match the housing of the mobile computing device. 
     Responsive to detecting a predetermined condition, such as sensing an approaching user finger, the color-controlled layer may be controlled to change color from an initial color to a second color. The color-controlled layer may be controlled to change color again upon contact of the finger, upon removal of the finger and upon determining authentication success. Authentication success may be determined by comparing the sensed fingerprint to a stored fingerprint template. The template may be stored on the device or on a server or cloud in communication with the device. 
     Other examples of a predetermined condition include a shaking of the computing device or a gesture. The shaking of the device may occur when the computing device is picked up and the color changes to indicate it has become active. A gesture could include any gesture known in the field of multi-touch gestures including but not restricted to a tap, a pinch, a flick, a long press and a rotate. Any of these gestures occurring in proximity, such as a hover mode, or in contact with the biometric sensor may cause the color of the color-controlled layer to be adjusted. 
     As the color-controlled layer is placed over or under the biometric sensor, the perceptible color of the sensor will change as the color of the color-controlled layer changes. 
     The color changing of the color-controlled layer may be based on temperature changes produced by thermal injection of the driver. 
     According to an aspect of the present disclosure, there is provided a method of controlling a perceived color of a biometric sensor that is a component of a mobile computing device. The method includes controlling a layer positioned over the biometric sensor to display an initial color that may be consistent with a color for a portion of a surface of the mobile computing device that surrounds the biometric sensor. In other aspects of the present application, a processor is provided for carrying out this method and a computer readable medium is provided for adapting a processor in a mobile computing device to carry out this method. 
     According to another aspect of the present disclosure, there is provided a method of changing a perceptible color of a biometric sensor in a computing device. The method includes detecting a predetermined condition and, responsive to the detecting, controlling a current flow provided to a color-controlled layer positioned in proximity to the biometric sensor to change the perceptible color from an initial color of the biometric sensor to a second color of the biometric sensor. In other aspects of the present application, a processor is provided for carrying out this method and a computer readable medium is provided for adapting a processor in a computing device to carry out this method. 
     According to another aspect of the present disclosure, there is provided a biometric scanning user interface. The biometric scanning user interface includes a layer including a plurality of heat-sensing elements, a multi-element layer positioned in proximity to the layer of heat-sensing elements, the multi-element layer including a plurality of heating elements and a plurality of thermochromic polymer elements and a driver adapted to control the plurality of heating elements to control a temperature of the multi-element layer to, thereby, control a color of the plurality of thermochromic polymer elements. The multi-element layer may be overlaid over the layer of heat-sensing element or may be placed underneath the layer of heat-sensing elements. The heat-sensing elements may include photovoltaic sensors for converting solar energy into direct current electricity. 
     In other aspects of the present disclosure, a method of changing a color of the thermochromic polymer elements within the biometric scanning user interface from an initial color to a second color is provided, as well as a processor for carrying out this method and a computer readable medium for executing steps to perform this method. The method of changing the color may occur upon detecting a predetermined condition, and responsive to the detecting, activating a driver to control the plurality of heating elements to control a temperature of the multi-element layer to, thereby, control a color of the plurality of thermochromic polymer elements. 
     Other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific implementations of the disclosure in conjunction with the accompanying figures. 
       FIG. 1  illustrates an anterior side of a mobile communication device  100 . Many features of the anterior side of the mobile communication device  100  are mounted within a housing  101  and include a display  126 , a speaker  111 , an anterior (user-facing) lens  103  and a multicolor fingerprint scanning interface  114 . 
     The mobile communication device  100  includes an input device and an output device (e.g., the display  126 ), which may comprise a full graphic, or full color, Liquid Crystal Display (LCD). 
     In some implementations, the input device and output device are combined, such as in the implementation illustrated in  FIG. 1 , wherein the display  126  comprises a touchscreen. In other implementations, the input device is a keyboard  224  (see  FIG. 2 ) having a plurality of keys. In touchscreen implementations, the keyboard  224  may comprise a virtual keyboard provided on the display  126 . Other types of output devices may alternatively be utilized. 
     The housing  101  may be elongated vertically, or may take on other sizes and shapes (including clamshell housing structures). In the case in which the keyboard  224  includes keys that are associated with at least one alphabetic character and at least one numeric character, the keyboard  224  may include a mode selection key, or other hardware or software, for switching between alphabetic entry and numeric entry. 
       FIG. 2  illustrates an example arrangement of internal components of the mobile communication device  100 . A processing device (a microprocessor  228 ) is shown schematically in  FIG. 2  as coupled between the keyboard  224  and the display  126 . The microprocessor  228  controls the operation of the display  126 , as well as the overall operation of the mobile communication device  100 , in part, responsive to actuation of the keys on the keyboard  224  by a user. 
     In addition to the microprocessor  228 , other parts of the mobile communication device  100  are shown schematically in  FIG. 2 . These may include a communications subsystem  202 , a short-range communications subsystem  204 , the keyboard  224  and the display  126 . The mobile communication device  100  may further include other input/output devices, such as a set of auxiliary I/O devices  206 , a serial port  208 , the speaker  111 , a microphone  212 , a biometric sensor (such as the multicolor fingerprint scanning interface  114  of  FIG. 1 ) and a proximity sensor  222 . The mobile communication device  100  may further include memory devices including a flash memory  216  and a Random Access Memory (RAM)  218  as well as various other device subsystems. The mobile communication device  100  may comprise a two-way, radio frequency (RF) communication device having voice and data communication capabilities. In addition, the mobile communication device  100  may have the capability to communicate with other computer systems via the Internet. 
     Operating system software executed by the microprocessor  228  may be stored in a computer readable medium, such as the flash memory  216 , but may be stored in other types of memory devices, such as a read only memory (ROM) or similar storage element. In addition, system software, specific device applications, or parts thereof, may be temporarily loaded into a volatile store, such as the RAM  218 . Communication signals received by the mobile device may also be stored to the RAM  218 . 
     The microprocessor  228 , in addition to its operating system functions, enables execution of software applications on the mobile communication device  100 . A predetermined set of software applications that control basic device operations, such as a voice communications module  230 A and a data communications module  230 B, may be installed on the mobile communication device  100  during manufacture. An authentication module  230 C may also be installed on the mobile communication device  100  during manufacture, to implement aspects of the present disclosure. As well, additional software modules, illustrated as an other software module  230 N, which may be, for instance, a Personal Information Manager (PIM) application, may be installed during manufacture. The PIM application may be capable of organizing and managing data items, such as e-mail messages, calendar events, voice mail messages, appointments and task items. The PIM application may also be capable of sending and receiving data items via a wireless carrier network  270  represented by a radio tower. The data items managed by the PIM application may be seamlessly integrated, synchronized and updated via the wireless carrier network  270  with the device user&#39;s corresponding data items stored or associated with a host computer system. 
     Communication functions, including data and voice communications, are performed through the communication subsystem  202  and, possibly, through the short-range communications subsystem  204 . The communication subsystem  202  includes a receiver  250 , a transmitter  252  and one or more antennas, illustrated as a receive antenna  254  and a transmit antenna  256 . In addition, the communication subsystem  202  also includes a processing module, such as a digital signal processor (DSP)  258 , and local oscillators (LOs)  260 . The specific design and implementation of the communication subsystem  202  is dependent upon the communication network in which the mobile communication device  100  is intended to operate. For example, the communication subsystem  202  of the mobile communication device  100  may be designed to operate with the Mobitex™, DataTAC™ or General Packet Radio Service (GPRS) mobile data communication networks and also designed to operate with any of a variety of voice communication networks, such as Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Personal Communications Service (PCS), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Wideband Code Division Multiple Access (W-CDMA), High Speed Packet Access (HSPA), Long Term Evolution (LTE) etc. Other types of data and voice networks, both separate and integrated, may also be utilized with the mobile communication device  100 . 
     Network access requirements vary depending upon the type of communication system. Typically, an identifier is associated with each mobile device that uniquely identifies the mobile device or subscriber to which the mobile device has been assigned. The identifier is unique within a specific network or network technology. For example, in Mobitex™ networks, mobile devices are registered on the network using a Mobitex Access Number (MAN) associated with each device and in DataTAC™ networks, mobile devices are registered on the network using a Logical Link Identifier (LLI) associated with each device. In GPRS networks, however, network access is associated with a subscriber or user of a device. A GPRS device therefore uses a subscriber identity module, commonly referred to as a Subscriber Identity Module (SIM) card, in order to operate on a GPRS network. Despite identifying a subscriber by SIM, mobile devices within GSM/GPRS networks are uniquely identified using an International Mobile Equipment Identity (IMEI) number. 
     When required network registration or activation procedures have been completed, the mobile communication device  100  may send and receive communication signals over the wireless carrier network  270 . Signals received from the wireless carrier network  270  by the receive antenna  254  are routed to the receiver  250 , which provides for signal amplification, frequency down conversion, filtering, channel selection, etc., and may also provide analog to digital conversion. Analog-to-digital conversion of the received signal allows the DSP  258  to perform more complex communication functions, such as demodulation and decoding. In a similar manner, signals to be transmitted to the wireless carrier network  270  are processed (e.g., modulated and encoded) by the DSP  258  and are then provided to the transmitter  252  for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the wireless carrier network  270  (or networks) via the transmit antenna  256 . 
     In addition to processing communication signals, the DSP  258  provides for control of the receiver  250  and the transmitter  252 . For example, gains applied to communication signals in the receiver  250  and the transmitter  252  may be adaptively controlled through automatic gain control algorithms implemented in the DSP  258 . 
     In a data communication mode, a received signal, such as a text message or web page download, is processed by the communication subsystem  202  and is input to the microprocessor  228 . The received signal is then further processed by the microprocessor  228  for output to the display  126 , or alternatively to some auxiliary I/O devices  206 . A device user may also compose data items, such as e-mail messages, using the keyboard  224  and/or some other auxiliary I/O device  206 , such as the navigation device  106 , a touchpad, a rocker switch, a thumb-wheel, a trackball, a touchscreen, or some other type of input device. The composed data items may then be transmitted over the wireless carrier network  270  via the communication subsystem  202 . 
     In a voice communication mode, overall operation of the device is substantially similar to the data communication mode, except that received signals are output to the speaker  111 , and signals for transmission are generated by a microphone  212 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the mobile communication device  100 . In addition, the display  126  may also be utilized in voice communication mode, for example, to display the identity of a calling party, the duration of a voice call, or other voice call related information. 
     The short-range communications subsystem  204  enables communication between the mobile communication device  100  and other proximate systems or devices, which need not necessarily be similar devices. For example, the short-range communications subsystem may include an infrared device and associated circuits and components, or a Bluetooth™ communication module to provide for communication with similarly-enabled systems and devices. 
     In overview, the present application describes controlling, with the microprocessor  228 , a perceived color for the multicolor fingerprint scanning interface  114  to be indicative of predefined conditions. 
     It is proposed herein to build the multicolor fingerprint scanning interface  144  to include multiple color elements. A perceived color for the multicolor fingerprint scanning interface  144  may be controlled, by, for example, a driver, by controlling current flow in rows and columns of the color-controlled layer. By controlling the perceived color for the color elements, the microprocessor  228  may control the perceived color for the multicolor fingerprint scanning interface  114 . 
     As an initial, default, condition, the microprocessor  228  may control (step  302 , see  FIG. 3 ) the color-controlled layer to display a first color that approximates a color for a portion of a surface of the mobile computing device that surrounds the biometric sensor. That is, in an example wherein the housing  101  is black, the microprocessor  228  may control the color-controlled layer to display black. 
     The material, from which the housing  101  is manufactured (e.g., plastic, glass, carbon fiber), may have an inherent gloss or other finish recognizable to the human eye. It is recognized that when the color-controlled layer is controlled to display black, the color-controlled layer will still be discernable from the housing  101 . However, it is considered that the user will have an improved impression of the mobile communication device  100 , as a whole, when the color-controlled layer is controlled to match the housing  101 , rather than contrast with the housing. 
     In practice, the microprocessor  228  may communicate with a sensor driver module (not shown). The sensor driver module may have an interrupt connected to the color-controlled layer. Upon receipt of a signal on the interrupt from the sensor driver module, a color change in the color-controlled layer may be implemented. The color change may be considered to be a global edit, with the color of the entire color-controlled layer changing in a uniform way. 
     The color change may also occur for a fixed period of time, after which the color may not change for a fixed period of time, or it may alternate with a subsequent color change for a fixed period of time. This will appear as the color flashing or rotating cyclically. 
     One condition under which the color of the color-controlled layer may be changed is when a user finger is approaching.  FIG. 4  illustrates example steps in a method of changing the color of the color-controlled layer responsive to a user finger approaching. The approach of the user finger may be sensed by the proximity sensor  222 . Responsive to sensing the approach of the user finger, the proximity sensor  222  may send an interrupt request (or IRQ) to the microprocessor  228  that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. 
     Responsive to receiving (step  402 ) the IRQ from the proximity sensor  222 , the microprocessor  228  may control (step  404 ) the color-controlled layer to display a second color. In one embodiment of the present application, rather than continuously displaying the second color, the microprocessor  228  may control the color-controlled layer to oscillate between displaying the second color and displaying the first, default, color. When the color is oscillating, each color may be displayed for a period of time having a corresponding duration. 
     Another condition under which the color of the color-controlled layer may be changed is when a user finger comes into contact with a surface over the multicolor fingerprint scanning interface  114 . To implement this optional aspect of the present application, a capacitive touch sensor (not shown) may overlay the color-controlled layer that, itself, overlays the multicolor fingerprint scanning interface  114 .  FIG. 5  illustrates example steps in a method of changing the color of the color-controlled layer responsive to a user finger contacting the surface over the multicolor fingerprint scanning interface  114 . 
     The contact of the user finger may be sensed by the capacitive touch sensor. Responsive to sensing the contact of the user finger, the capacitive touch sensor may send an IRQ to the microprocessor  228 . Responsive to receiving (step  502 ) the IRQ from the capacitive touch sensor, the microprocessor  228  may control (step  504 ) the color-controlled layer to display a third color. 
     A further condition under which the color of the color-controlled layer may be changed is when a user finger ends contact with the surface over the multicolor fingerprint scanning interface  114 .  FIG. 6  illustrates example steps in a method of changing the color of the color-controlled layer responsive to a user finger ending contact with the surface over the multicolor fingerprint scanning interface  114 . 
     The end of contact of the user finger may be sensed by the capacitive touch sensor. Responsive to sensing the end of contact of the user finger, the capacitive touch sensor may send an IRQ to the microprocessor  228 . Responsive to receiving (step  602 ) the IRQ from the capacitive touch sensor, the microprocessor  228  may control (step  604 ) the color-controlled layer to display a fourth color. 
     Still further conditions under which the color of the color-controlled layer may be changed relate to a result of an authentication of the fingerprint sensed by the multicolor fingerprint scanning interface  114 .  FIG. 7  illustrates example steps in a method of changing the color of the color-controlled layer dependent upon success of authentication. 
     Responsive to determining (step  702 ) that fingerprint authentication has been successful, the microprocessor  228  may control (step  704 ) the color-controlled layer to display a fifth color. In contrast, responsive to determining (step  702 ) that fingerprint authentication has been unsuccessful, the microprocessor  228  may control (step  706 ) the color-controlled layer to display a sixth color. 
     In addition to a color change upon successful authentication, an additional operation may be performed. This operation could include unlocking the device and discontinuing the current flow provided to the control-controlled layer such that no color change occurs. Additional color changes may also occur in response to specific notifications. For example, a specific color may be identified to correspond to an email notification, or a phone call, or an application update. 
     Thus far, it has been discussed that the color-controlled layer may be controlled to change color. The following provides an example of the manner in which the color-controlled layer may be structured so that the color-controlled layer may be so controlled. 
     The multicolor fingerprint scanning interface  114  may, for example, operate, at least in part, based on a thermal technique that has been known in the fingerprint capture industry for over a decade. A principle of operation of example fingerprint sensors that use the thermal technique may rely on the fact that, according to the so-called “active thermal proximity principle,” the example fingerprint sensor produces regular bursts of heat when sensing a fingerprint. 
       FIG. 8  illustrates, in cross-section, a finger  800  and an example fingerprint sensor  806 . The finger  800  is known to have a fingerprint that is defined by ridges  802  and valleys  804 . The example fingerprint sensor  806  includes a sensor driver  812  in communication with a layer of heating elements  810  and a layer of sensing elements  808 . The layer of heating elements  810  overlays the layer of sensing elements  808 . 
     More particularly, in the case wherein the finger  800  is in contact with the example fingerprint sensor  806 , the heating elements  810  are controlled, by the sensing element, to generate heat. Where a fingerprint is in contact with the example fingerprint sensor  806 , some of the heat generated by a first heating element  810  is absorbed by, or otherwise transferred to, the fingerprint ridge  802 . A first sensing element  808  in close proximity to the first heating element  810  may indicate, to the sensor driver  812 , a first sensed temperature. While the same fingerprint remains in contact with the fingerprint sensor, some of the heat generated by a second heating element is not absorbed, or otherwise transferred to, the fingerprint, since the second heating element is proximate to a valley  804  rather than a ridge  802 . A second sensing element  808  in close proximity to the second heating element  810  may indicate, to the sensor driver  812 , a second sensed temperature. On the basis of the second sensed temperature being greater than the first sensed temperature, since the second sensed temperature corresponds to a valley, the example fingerprint sensor  806  may identify a location for a ridge  802  and a valley  804 . Based on additional temperatures reported by additional sensing elements  808 , the example fingerprint sensor  806  may begin to determine the location of many ridges  802  and valleys  804  to generate a representation for a sensed fingerprint of the finger  800 . 
     In overview, it is proposed herein to construct the multicolor fingerprint scanning interface  114  by including, in a layer of heating elements, thermochromic polymer elements in a manner such that there is no overlap, nor any interference, between the heating elements and the thermochromic polymer elements. 
     Thermochromic polymer elements are known to implement a change of color responsive to temperature change. Accordingly, through control of the temperature of the thermochromic polymer elements, the perceived color of the multicolor fingerprint scanning interface  114  may be controlled. 
       FIG. 9  illustrates, in cross-section, an example structure for the multicolor fingerprint scanning interface  114 . The multicolor fingerprint scanning interface  114  includes a sensor driver  912  in communication with a mixed-element layer  916  and a layer of sensing elements  908 . The mixed-element layer  916  overlays the layer of sensing elements  908 . The mixed-element layer  916  includes heating elements  910  and thermochromic polymer elements  914 . 
     The thermochromic polymer elements  914  may be implemented as flexible, epoxy elements that are, for example, approximately 25 microns thick. The thermochromic polymer elements  914  may be formed, for example, from a Leuco Dye-Developer-Solvent. 
     The first tests to apply thermo-responsive dyes in thermally activated systems were described in 1992. The introduced allyl aryl ethers rearrange at 180° C. to a phenol lactone, which, in turn, undergoes intramolecular proton migration to provide a colored surface. However, nonsufficient cycle number and missing switching temperatures in a practically useful range prevented its use. Therefore, leuco dye-developer complexes became important systems to achieve thermochromic properties for different polymer materials by endowing a separate phase of the thermochromic system in a non-thermochromic polymer matrix. Binary and ternary mixtures are used to enable thermochromic switching from a colorless state into a multicolored state. 
     A distinguishing feature of these mixtures is a strong attractive interaction between LG and LCA, leading to the formation of a colorless congruently melting compound of the form (LG)2-LCA. In the molten state, the attractive interaction between LG and the LCA is relatively weak, and the stronger interaction is between LG and CVL, producing a colored complex of the form (LG)x-CVL (x=3-9). However, upon solidification during slow cooling, the color developer LG moves from the colored (LG)x-CVL to a colorless (LG)2-LCA complex, leading to the decolorization of the mixture. Effectively, the long chain alcohol works not only as the solvent but also as a “decolorization agent” by “disabling the color developer” through complexation. 
       FIG. 10  illustrates, in plan view, the mixed-element layer  916  of  FIG. 9 . As illustrated in  FIG. 10 , the heating elements  910  are dispersed about the mixed-element layer  916  among the thermochromic polymer elements  914 . In the example layout of the mixed-element layer  916  that is illustrated in  FIG. 10 , each of the heating elements  910  is surrounded by thermochromic polymer elements  914 . As described herein above, the heating elements  910  may be controlled by the sensor driver  912 . 
     On one hand, heating elements  910  may be controlled by the sensor driver  912  for the purposes, described hereinbefore, of obtaining a fingerprint using the sensing elements  908 . On the other hand, when there is no activity in the sensing elements  908 , the heating elements  910  may be controlled by the sensor driver  912  for the purposes of increasing the temperature of the thermochromic polymer elements  914  to induce a change in the polymer, thereby changing the color of the surface of the multicolor fingerprint scanning interface  114 . 
     To comprehend the color change associated with temperature change, one may visualize a simple aquarium thermometer. A simple aquarium thermometer may cost around 11 cents to manufacture and controlling temperature range per color is accomplished using a simple polymer doping process. 
     Example correspondence between color and temperature is illustrated in the following table: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Temperature  
                   
               
               
                   
                 (degrees Celsius) 
                 Color 
               
               
                   
                   
               
             
            
               
                   
                 46.75 
                 Green 
               
               
                   
                 46.83 
                 Blue 
               
               
                   
                 47.09 
                 Yellow 
               
               
                   
                 47.24 
                 Grey 
               
               
                   
                   
               
            
           
         
       
     
     Notably, a designer of the mobile communication device  100  that includes the multicolor fingerprint scanning interface  114  is encouraged to consider decoupling the heat dissipation coming from the inside of the mobile communication device  100  and generated by, e.g., a power amplifier, a battery and various integrated circuits. For example, failing to keep the temperature of the multicolor fingerprint scanning interface  114  below 46.00 degrees Celsius may cause the mixed-element layer  916  to display multiple colors simultaneously. 
     Although throughout the foregoing, the multicolor fingerprint sensing interface  114  has been discussed in terms of a fingerprint sensor, the person of ordinary skill in the art will understand that other biometric sensors may be adapted for a color-controlled appearance in a similar manner. Indeed, rather than a fingerprint being scanned, the biometric being scanned may be, for a mere two further examples, a palm print or an ear print. 
     The above-described implementations of the present application are intended to be examples only. Alterations, modifications and variations may be effected to the particular implementations by those skilled in the art without departing from the scope of the application, which is defined by the claims appended hereto.