Patent Publication Number: US-2023152448-A1

Title: Ultrasonic touch sensor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 102021129855.5 filed on Nov. 16, 2021, the content of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     In many fields of application, interaction of a user with an electronic system is required. For example, in a motor vehicle, a switch is used for actuating the windshield ventilation and a corresponding display is used. Often, touch sensors are used as the switch. Capacitive touch sensors are subject to restrictions in terms of the material of the surface on which they are intended to detect touching. For example, a combination of a metallic touch face with a capacitive touch sensor is not generally possible. In ultrasonic touch sensors, the touch face may consist of various materials. However, good acoustic coupling to the touch face is necessary in order to identify touching reliably. 
     SUMMARY 
     An object of the present implementation is to provide an ultrasonic touch sensor which allows particularly reliable detection of touching, which can be achieved by the subject-matter of one or more claims, as well as example implementations described in the following description. 
     An ultrasonic touch sensor is provided, having a contact face for applying the ultrasonic touch sensor onto a covering, having a first ultrasonic transducer element, having a first semiconductor chip, the first semiconductor chip including the first ultrasonic transducer element, and having a second ultrasonic transducer element, wherein an acoustic barrier is formed between the first ultrasonic transducer element and the second ultrasonic transducer element. 
     A method for producing an ultrasonic touch sensor is likewise disclosed, wherein a first semiconductor chip is provided, wherein the first semiconductor chip including a first ultrasonic transducer element, wherein a second ultrasonic transducer element is provided, wherein the first semiconductor chip is embedded in a potting compound, wherein a recess is introduced into the potting compound, in particular using laser ablation, in order to produce an acoustic barrier between the first ultrasonic transducer element and the second ultrasonic transducer element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of one or more ultrasonic touch sensors and of one or more methods will now be explained in more detail with the aid of the drawing. In the drawings: 
         FIG.  1    shows an ultrasonic transducer element; 
         FIG.  2    shows an ultrasonic transducer element; 
         FIG.  3    shows an ultrasonic transducer element in a first situation; 
         FIG.  4    shows the ultrasonic transducer element shown in  FIG.  3    in a second situation; 
         FIG.  5    shows an ultrasonic transducer element in a third situation; 
         FIG.  6    shows the ultrasonic transducer element shown in  FIG.  5    in a fourth situation; 
         FIG.  7    shows an ultrasonic touch sensor; 
         FIG.  8    shows a step for a production of an ultrasonic touch sensor 
         FIG.  9    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  10    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  11    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  12    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  13    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  14    shows a step for the production of an ultrasonic touch sensor; 
         FIG.  15    shows an ultrasonic touch sensor; 
         FIG.  16    shows an ultrasonic touch sensor; 
         FIG.  17    shows an ultrasonic touch sensor; and 
         FIG.  18    shows a flowchart for the production of an ultrasonic touch sensor. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1  and  2    represent an ultrasonic transducer element  100 . The ultrasonic transducer element  100  comprises a diaphragm  120  with an electrode  112 , and a substrate  101  with an electrode  111 . A cavity  130 , which allows movement of the diaphragm  120 , is provided between the diaphragm  120  and the substrate  101 . 
     By applying an AC voltage between the electrodes  111  and  112  using a voltage source  151 , the diaphragm  120  can be excited in oscillation so that the ultrasonic transducer element  100  can emit ultrasound waves  141 . 
     The ultrasonic transducer element  100  shown in  FIGS.  1  and  2    may likewise be used to detect ultrasound waves  142 . For this purpose, a DC voltage may be applied between the electrodes  111  and  112  using the voltage source  152 . The ultrasound waves  142  can excite the diaphragm  120  in oscillation. An AC voltage is induced because of the distance which therefore varies between the electrodes  111  and  112 , and can be measured using a measuring device  153 . 
       FIGS.  3  to  6    schematically represent the way in which touching of a covering  390 ,  490  (e.g., a cover or lid) on the opposite side of the covering  390 ,  490  from the ultrasonic touch sensor can be registered using the ultrasonic transducer element  311  or  411 , respectively. The ultrasonic transducer element  311  or  411  is respectively embedded in an encapsulation layer  320 ,  420 , the encapsulation layer  320 ,  420  comprising a contact surface via which the ultrasonic touch sensor is applied on the covering  390 ,  490 . The ultrasonic transducer element  311 ,  411  may respectively be fastened on a circuit board  370 ,  470  and electrically connected thereto. 
     As shown in  FIG.  3   , ultrasound waves can be generated using the ultrasonic transducer element  311 , these being transmitted substantially fully through the interface between the encapsulation layer  320  and the covering  390  and subsequently reflected at the free surface of the covering  390  on the opposite side from the encapsulation layer  320 . After transmission back through the interface between the covering  390  and the encapsulation layer  320 , the ultrasound waves can again be detected by the sensor element  311  so that an echo signal as represented below  FIG.  3    is obtained. 
     If the free surface of the covering  390  on the opposite side from the encapsulation layer  320  is touched, for example with a finger  401 , only a small proportion of the ultrasound waves will be reflected at the free surface and the echo signal will decrease, as represented below  FIG.  4   . 
       FIG.  5    shows that a cavity  491  remains when the ultrasonic touch sensor is applied on the covering  490 . The effect of this cavity  491  is that the ultrasound waves emitted by the sensor element  411  do not pass through the interface between the encapsulation layer  420  and the covering  490 , but are reflected at this interface so that an echo signal as represented underneath is obtained. 
     Since the ultrasound waves are not (or are almost not) transmitted into the covering, touching the covering  490  with the finger  601  does not lead to a change in the echo signal. 
     Although a capacitive sensor element  311 ,  411  has been described above, corresponding considerations also apply for a piezoelectric sensor element, in particular for ultrasonic transceivers which operate according to a piezoelectric measurement principle. 
       FIG.  7    illustrates an ultrasonic touch sensor  701  that comprises a housing  702  in which a first semiconductor chip  711  and a second semiconductor chip  712  are arranged. The first semiconductor chip  711  and the second semiconductor chip  712  in this case respectively comprise an ultrasonic transducer element and are embedded in an encapsulation layer  706 . The ultrasonic touch sensor  701  is connected to a covering  703  using an adhesive layer  704 . 
     When ultrasound waves are emitted by an ultrasonic transducer element, reflections may occur at the housing  702  so that not only a variable echo signal  780  due to touching with the finger  705  but also possibly parasitic ultrasound signals  771 ,  772 ,  773 ,  774  are registered. These may interfere with the reliable registering of touching of the covering  703 . 
       FIG.  8    illustrates a step for the production of a touch sensor. A prefabricated housing  801  having a recess  802  and having electrical terminals  811 ,  812  is provided. 
     As represented in  FIG.  9   , a first semiconductor chip  921  and a second semiconductor chip  922  may be arranged in the recess  802  of the prefabricated housing  801 . Using bonding wires  931  and  932 , electrical contacts of the first semiconductor chip  921  and of the second semiconductor chip  922  may be connected to the electrical terminals  811 ,  812 . The first semiconductor chip  921  may comprise a first ultrasonic transducer element and the second semiconductor chip  922  may comprise a second ultrasonic transducer element. 
     The first ultrasonic transducer element and the second ultrasonic transducer element may respectively be covered with a gel  1041 ,  1042  for acoustic coupling to a potting compound. The applied gel  1041 ,  1042  may be subjected to a physical and/or chemical treatment so that a cured gel  1141 ,  1142  is obtained, as represented in  FIG.  11    by darker hatching. 
     Subsequently, the first semiconductor chip  921  and the second semiconductor chip  922  may be embedded in a potting compound  1205  (cf.  FIG.  12   ), which may then be subjected to a physical and/or chemical treatment, in particular cured, as represented in  FIG.  13    by the darker hatching. 
     The potting compound  1305  may in this case, in particular, protect the bonding wires  931 ,  932  and their fastening on the first semiconductor chip  921  or respectively the second semiconductor chip  922  and on the electrical terminals  811 ,  812  from mechanical stress. Via the free surface of the potting compound  1305 , the ultrasonic transducer element may later be applied onto a covering. 
     As represented in  FIG.  14   , a recess  1406  is then introduced into the potting compound  1305  in order to produce an acoustic barrier between the first semiconductor chip and the second semiconductor chip. This may, for example, be carried out using laser ablation. 
       FIG.  15    shows an ultrasonic touch sensor  1500  having a contact face for applying the ultrasonic touch sensor  1500  onto a covering  1592 , having a first ultrasonic transducer element, having a first semiconductor chip  921 , the first semiconductor chip  921  comprising the first ultrasonic transducer element, and having a second ultrasonic transducer element, wherein an acoustic barrier  1406  is formed between the first ultrasonic transducer element and the second ultrasonic transducer element. The second ultrasonic transducer element is in this case arranged laterally with respect to the first ultrasonic transducer element. In the ultrasonic touch sensor  1500  in  FIG.  15   , the acoustic barrier  1406  is formed as a cavity, in particular as an air gap. It is, however, also conceivable for the acoustic barrier to comprise an absorption material. In particular, polymers comprising tungsten may be used as an absorption material. It is likewise conceivable to provide the recess  1406  with a sound-absorbing wall structure in order to produce the acoustic barrier. In order to fasten the ultrasonic touch sensor  1500 , the covering  1592  may comprise an adhesive layer  1591 . 
     Using the acoustic barrier, it is possible to reduce the risk that parasitic ultrasound sources  1571 ,  1572 , which are undesired but often difficult to avoid, and which occur during the emission of ultrasound waves  1581  by the first ultrasonic transducer element in the direction of the covering  1592 , will reach the second ultrasonic transducer element. In particular, crosstalk may be avoided. The reliability of the detection of the touching of the covering  1592  with a finger  1505  may therefore be increased. 
       FIG.  16    represents a further ultrasonic touch sensor  1600 . It corresponds substantially to the ultrasonic touch sensor  1500  which is represented in  FIG.  15   , so that for the description of the features provided with the reference numerals  1611 ,  1631 ,  1621 ,  1641 ,  1681 ,  1605 ,  1601 ,  1606 ,  1691 ,  1682 ,  1642 ,  1622 ,  1692 ,  1632 ,  1612 , reference is made to the description of the corresponding features  811 ,  931 ,  921 ,  1141 ,  1581 ,  1305 ,  801 ,  1406 ,  1591 ,  1582 ,  1142 ,  922 ,  1592 ,  932 ,  812 . 
     In addition to the first semiconductor chip  1621  and the second semiconductor chip  1622 , the ultrasonic touch sensor  1600  also comprises a third semiconductor chip  1623 . The third semiconductor chip  1623  may, in particular, comprise an integrated circuit for generating the control signals for a transmitting ultrasonic transducer element and/or for evaluating the reception signal for a receiving ultrasonic transducer element. The use of a third semiconductor chip  1623  may make it possible to manufacture the third semiconductor chip  1623  with process techniques that differ from the process techniques which are needed for the production of the ultrasonic transducer elements. 
     The third semiconductor chip  1623  may be provided as a semiconductor chip  1623  partially or fully embedded in the prefabricated housing. The third semiconductor chip  1623  may also be arranged laterally with respect to or even below the first semiconductor chip  1612 . 
     A further ultrasonic touch sensor  1700  is depicted in  FIG.  17   . In contrast to the ultrasonic touch sensors  1500  and  1600 , in the ultrasonic touch sensor  1700  a plurality of ultrasonic transducer elements are arranged in a single semiconductor chip  1721 . A plurality of acoustic barriers  1761 ,  1762 ,  1763 ,  1764 ,  1765 ,  1766 ,  1767  are provided between the ultrasonic transducer elements. The acoustic barriers  1761 ,  1762 ,  1763 ,  1764 ,  1766 ,  1767  are formed as recesses which extend not only through the potting compound  1705  but also through the gel  1741  that covers the ultrasonic transducer elements. The plurality of ultrasonic transducer elements separated by the acoustic barriers  1761 ,  1762 ,  1763 ,  1764 ,  1766 ,  1767  can make it possible to determine not only touching, but also a position of the finger  1505 . The ultrasonic touch sensor  1700  may consequently also be regarded as a position sensor. 
       FIG.  18    illustrates steps for the production of an ultrasonic touch sensor. In step  1801 , a first semiconductor chip is provided, the first semiconductor chip comprising a first ultrasonic transducer element. In step  1802 , a second ultrasonic transducer element is provided. In step  1803 , the first semiconductor chip is embedded in a potting compound. In step  1804 , a recess is introduced into the potting compound in order to produce an acoustic barrier between the first ultrasonic transducer element and the second ultrasonic transducer element. 
     ASPECTS 
     Some aspect implementations will be defined by the following aspects: 
     Aspect 1. An ultrasonic touch sensor ( 1500 )
         having a contact face for applying the ultrasonic touch sensor ( 1500 ) onto a covering ( 1592 ),   having a first ultrasonic transducer element,   having a first semiconductor chip ( 921 ), the first semiconductor chip ( 921 ) comprising the first ultrasonic transducer element,   having a second ultrasonic transducer element,   wherein an acoustic barrier is formed between the first ultrasonic transducer element and the second ultrasonic transducer element.       

     Aspect 2. The ultrasonic touch sensor ( 1500 ) as according to Aspect 1,
         wherein the second ultrasonic transducer element is arranged laterally with respect to the first ultrasonic transducer element.       

     Aspect 3. The ultrasonic touch sensor ( 1500 ) as according to one of Aspects 1 or 2,
         wherein the acoustic barrier is formed as a cavity, in particular as an air gap.       

     Aspect 4. The ultrasonic touch sensor ( 1700 ) as according to one of Aspects 1 to 3,
         having a second semiconductor chip ( 922 ),   wherein the second semiconductor chip ( 922 ) comprises the second ultrasonic transducer element.       

     Aspect 5. The ultrasonic touch sensor ( 1500 ) as according to one of Aspects 1 to 3,
         wherein the first semiconductor chip comprises the second ultrasonic transducer element.       

     Aspect 6. The ultrasonic touch sensor ( 1500 ) as according to one of the preceding aspects,
         wherein the first ultrasonic transducer element and/or the second ultrasonic transducer element is covered with a gel for acoustic coupling to a potting compound.       

     Aspect 7. The ultrasonic touch sensor ( 1500 ) as according to one of the preceding aspects,
         wherein the first semiconductor chip ( 921 ) and/or the second semiconductor chip ( 922 ) is embedded in a or the potting compound ( 1305 ).       

     Aspect 8. The ultrasonic touch sensor ( 1500 ) as according to Aspect 7,
         wherein the barrier has an acoustic impedance which differs from the acoustic impedance of the potting compound.       

     Aspect 9. The ultrasonic touch sensor ( 1500 ) as according to one of Aspects 5 to 8,
         wherein the first semiconductor chip comprises a multiplicity of ultrasonic transducer elements, which are separated from one another by acoustic barriers.       

     Aspect 10. The ultrasonic touch sensor ( 1500 ) as according to one of the preceding aspects,
         wherein the ultrasonic touch sensor ( 1500 ) is a position sensor.       

     Aspect 11. A method for producing an ultrasonic touch sensor ( 1500 ), in particular an ultrasonic touch sensor ( 1500 ) as according to one of Aspects 1 to 10,
         wherein a first semiconductor chip ( 921 ) is provided,   wherein the first semiconductor chip ( 921 ) comprises a first ultrasonic transducer element,   wherein a second ultrasonic transducer element is provided,   wherein the first semiconductor chip ( 921 ) is embedded in a potting compound ( 1205 ),   wherein a recess ( 1406 ) is introduced into the potting compound ( 1305 ), in particular using laser ablation, in order to produce an acoustic barrier between the first ultrasonic transducer element and the second ultrasonic transducer element.       

     Aspect 12. The method for producing an ultrasonic touch sensor ( 1500 ) as according to Aspect 11,
         wherein a prefabricated housing ( 801 ) is provided,   wherein a first semiconductor chip ( 921 ) is arranged in a recess ( 802 ) of the prefabricated housing ( 801 ).       

     Aspect 13. The method for producing an ultrasonic touch sensor ( 1500 ) as according to one of Aspects 11 or 12,
         wherein the first ultrasonic transducer element and/or the second ultrasonic transducer element is covered with a gel ( 1041 ) for acoustic coupling to the potting compound ( 1305 ).       

     Aspect 14. The method for producing an ultrasonic touch sensor ( 1500 ) as according to Aspect 13,
         wherein the gel ( 1141 ) is cured.       

     Aspect 15. The method for producing an ultrasonic touch sensor ( 1500 ) as according to one of Aspects 11 to 14,
         wherein the potting compound ( 1305 ) is cured.       

     Aspect 16. The method for producing an ultrasonic touch sensor ( 1500 ) as according to one of Aspects 11 to 15,
         the recess ( 1406 ) is filled with an absorption material in order to produce the acoustic barrier.       

     Although specific aspect implementations have been illustrated and described in this description, persons with normal technical knowledge will realize that many alternative and/or equivalent implementations may be selected in place of the specific aspect implementations which are presented and described in the description, without departing from the scope of the implementation as presented. The intention is for this application to cover all adaptations or variations of the specific aspect implementations that are discussed herein. It is therefore intended for this implementation to be limited only by the claims and the equivalents of the claims.