Abstract:
A sensor packaging system and methodology includes a plastic substrate configured to include a gap for receiving and maintaining an acoustic wave sensor. An antenna can be printed directly on the plastic substrate and connected electrically to the acoustic wave sensor for the transmission and receipt of data from and to the acoustic wave sensor. The antenna can be flip chip mounted to the acoustic wave sensor, which can be implemented, for example, in the context of a Surface Acoustic Wave (SAW) sensor chip. Such a SAW sensor chip can includes a plurality of metal electrodes located on the same surface of the plastic substrate as the SAW sensor chip.

Description:
TECHNICAL FIELD  
       [0001]     Embodiments are generally related to sensing devices and methods thereof. Embodiments are also related to wireless sensors. Embodiments are additionally related to surface acoustic wave sensors utilized in pressure sensing applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     Wireless sensors are utilized in a number of sensing applications, including, for example, pressure and temperature sensing in automobile tires. Wireless sensors are typically mounted in association with antenna and receiving units. In recent years, for example, like a mobile communication unit such as a cellular phone, or a wireless LAN (Local Area Network) based on the so-called IEEE (Institute of Electronic and Electronics Engineers) 802.11 standard, various wireless communication techniques have been remarkably developed, and in accordance with this, various techniques concerning an antenna element as an inevitably provided member to perform wireless communication have also been developed.  
         [0003]     As an antenna element, for example, one in which a radiation electrode, a surface electrode or the like is formed on a cylindrical dielectric is known. This kind of antenna element is generally installed at the outside of an equipment body and is used. However, in the antenna element of such a type that it is disposed at the outside and is used, there are problems that miniaturization of the equipment is obstructed, high mechanical strength is required, and the number of parts is increased.  
         [0004]     A problem with conventional wireless sensor technology is that it is difficult to integrate the antenna on the wireless sensor chip for operation frequencies lower than 2.4 GHz. A need exists for a robust technology for chip level packaging and antenna and impedance matching circuit fabrication on a flexible substrate. An example where a need for an improved wireless sensor packaging system and methodology exists is in the area of wireless tire pressure sensing. A system and methodology that meets this continuing need is disclosed in greater detail herein.  
       BRIEF SUMMARY  
       [0005]     The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.  
         [0006]     It is, therefore, one aspect of the present invention to provide for an improved wireless sensing device including two parts bonded one to the other and an associated antenna.  
         [0007]     It is another aspect of the present invention to provide for an improved wireless acoustic wave sensor.  
         [0008]     It is yet another aspect of the present invention to provide for a system for packaging a wireless acoustic wave sensor and an associated antenna. Such an acoustic wave sensor can be configured from two components bonded together by varying technologies, such as, for example glass frit, plastic, or direct bonding.  
         [0009]     The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A sensor packaging system and methodology are described herein, that generally includes a plastic substrate configured to include a gap for receiving and maintaining an acoustic wave sensor. An antenna can be printed directly on the plastic substrate and connected electrically to the acoustic wave sensor for the transmission and receipt of data from and to the acoustic wave sensor. The antenna can be “flip chip” mounted to the acoustic wave sensor, which can be implemented, for example, in the context of a Surface Acoustic Wave (SAW) sensor chip. Such a SAW sensor chip can includes a plurality of metal electrodes located on the surface of quartz wafer. In addition, such a SAW sensor can be configured with a quartz cover and the SAW quartz chip may be bonded one to the other utilizing, for example, glass frit technology, so that an all quartz packaging (AQP) configuration, also referred to as “zero level packaging” can be obtained. Such a glass frit technology can be applied to any type of quartz SAW sensor packaging, where a low stress robust packaging technology is desired. Depending on application requirements, any type of low stress quartz-to quartz bonding can be utilized, such as, for example, direct quartz-to-quartz bonding, plastic bonding, etc.  
         [0010]     An insulating polyimide can be utilized to selectively encapsulate one or more surfaces of the SAW sensor chip. A sensing diaphragm is generally maintained by the SAW sensor chip. The sensing diaphragm can be configured to include a recessed area. A gel that functions as a pressure transmitting element can be located within the recessed area. The plastic substrate can be configured as a dielectric substrate, which is flexible. The acoustic wave sensor generally includes a quartz cover and the gap formed in the plastic substrate accommodates the quartz cover. The antenna is printed directly on the plastic substrate by maskless ink-jet deposition. Additionally, the acoustic wave sensor can be mounted on the antenna with a plurality of bonding pads associated with the acoustic wave sensor positioned on a plurality of corresponding bonding pads associated with the antenna.  
         [0011]     The sensor packaging system disclosed herein thus includes a dielectric substrate and a wireless acoustic wave sensor comprising at least one quartz component. An antenna is generally attached to the wireless acoustic wave sensor on the dielectric substrate utilizing ink-jet maskless printing, thereby providing a sensor for the wireless transmission and receipt of sensor data. The antenna printed on the dielectric substrate preferably operates in a frequency range of approximately 100 KHz to 2.4 GHz. The dielectric substrate comprises a hole for maintaining the wireless acoustic wave sensor, wherein the hole is configured so that a quartz cover associated with the wireless acoustic wave sensor can be accommodated therein for a decreased total thickness of the acoustic wave sensor.  
         [0012]     The system and methodology disclosed herein thus relates to a technology for the chip level packaging of the wireless SAW sensors. A direct writing technology for the antenna and impedance matching circuit fabrication on a plastic substrate can be combined with the flip chip technology for attaching the antenna chip to the wireless SAW quartz sensor chip. Metal layers for printed antenna and matching circuit, vias filling and final plastic housing of the packaged wireless sensor can be accomplished utilizing a maskless, ink-jet printing process. This technology can be adapted for use with any type of wireless sensor that includes an antenna external to the sensor chip.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.  
         [0014]      FIG. 1  illustrates a side view of a glass fritted all quartz packaged surface acoustic wave sensor that can be implemented in accordance with a preferred embodiment;  
         [0015]      FIG. 2  illustrates a side view of antenna printing on a plastic substrate configured with a gap therein, in accordance with a preferred embodiment;  
         [0016]      FIG. 3  illustrates a side view of a wireless acoustic wave sensor system, which can be implemented in accordance with a preferred embodiment; and  
         [0017]      FIG. 4  illustrates a perspective view of a maskless ink-jet deposition printing system, which can be adapted for use in accordance with a preferred embodiment.  
     
    
     DETAILED DESCRIPTION  
       [0018]     The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.  
         [0019]      FIG. 1  illustrates a side view of a surface acoustic wave sensor  100  that can be implemented in accordance with a preferred embodiment. The surface acoustic wave sensor  100  depicted in  FIG. 1  can be implemented as a quartz-based Surface Acoustic Wave (SAW) sensor chip and generally includes a one or more SAW sensors  104 ,  106 ,  108 , which are connected to and maintained by a SAW quartz chip  110 . The sensor  100  also includes a diaphragm  102  that is maintained by the SAW quartz chip  110 . A reference chamber  114  can be located between the SAW quartz chip  110  and a quartz cover  112 .  
         [0020]     In accordance with a preferred embodiment, the hermetic sealing of the SAW quartz chip  110  and the quartz cover  112  can be accomplished utilizing glass frit technology, in which a glass wall closes the reference pressure chamber of the sensor. The glass frit spacers  122  and  124  depicted in  FIG. 1  represent schematically the glass frit process, which allows the metal electrodes  126  and  128  to be located outside of the reference chamber  114  while still preserving the hermetic structure of the pressure chamber. Metal electrodes  126  and  128  are also supported by the SAW quartz chip  110  and are respectively separated from the quartz cover  112  by glass frit spacers  122  and  124 . Metal-to-metal flip chip components  114 ,  116  and  118 ,  120  are respectively connected to the metal electrodes  126  and  128 .  
         [0021]      FIG. 2  illustrates a side view of an antenna  204 ,  205  printed on a plastic substrate  206  configured with a gap or hole  202  therein, in accordance with a preferred embodiment. Note that in  FIGS. 1-4 , identical or similar parts or elements are generally indicated by identical reference numerals. The hole  202  is formed in plastic substrate  206  in order to accommodate the quartz cover  112 . Metal-to-metal surface mounting components  114  and  120 , which are often referred to as so-called “bumps” by those skilled in the art are also depicted in  FIG. 2 . Existing flip chip technology can be applied for the realization of conductive bumps on a plastic substrate necessary for the connection of the sensor pad to the antenna. The bumps  114  and  120  may possess, for example, a diameter of approximately 100 micrometers, and can be configured from metal or conductive polymers. Antenna  204 ,  205  can be configured from metal, conductive plastic or a combination thereof, depending upon design considerations.  
         [0022]      FIG. 3  illustrates a side view of a wireless acoustic wave sensor system  300 , which can be implemented in accordance with a preferred embodiment. System  300  generally includes the plastic substrate  206  depicted in  FIG. 3  and is surrounded by a polyimide layer  304  and a polyimide layer  306 . One or more polyimide via fillings  308  and  309  are also provided between portions of the plastic substrate  206 . Antenna components  310 ,  312  and  314  depicted in  FIG. 3  form the antenna  205  depicted in  FIG. 2 , while antenna components  316 ,  318  and  320  forms the antenna  204  depicted in  FIG. 2 .  
         [0023]     The resulting sensor or system  300  can be implemented in the context of any type of wireless sensor where an antenna such as antenna  204 ,  205  and associated antenna components  310 ,  312 ,  314  and  315 ,  318 ,  320  are attached to the output of sensor  300 . The configuration depicted in  FIG. 1 , for example, demonstrates chip level packaging of the wireless SAW quartz sensor  100  for pressure measurement, where a region with thinned quartz is utilized to implement the pressure sensing diaphragm  102 . The interrogation signal comes to the sensor antenna  204 ,  205  and the sensor response (echo) is transmitted back to the sensor antenna  204 ,  205 , which can further send the electromagnetic signal to a sensor interrogator. The antenna  204 ,  205  can be fabricated by ink-jet technology (i.e., see  FIG. 4 ) on the plastic substrate  206  followed by surface mounting of the antenna chip to the sensor chip by the flip chip technology and finishing with the final housing of the sensor  100  with a plastic layer.  
         [0024]     The new aspect of the antenna fabrication for wireless sensors is the application of the technology for the metal deposition by ink-jet deposition of the metal layer as indicated in  FIG. 2 . Thus, the wire antenna with potential reliability problems can be eliminated. In addition, the circuit for impedance matching can be also performed by means of this ink-jet technology, where the passive circuit can be printed on the dielectric substrate. The layout of the sensor antenna  204 ,  205  can be obtained from electrical and magnetic simulations, where the operation frequency, gain and input impedance are generally responsible for the size of the antenna  204 ,  205 .  
         [0025]     The selective deposition of the metal layers for the formation of antenna  204 ,  205  can be accomplished utilizing a maskless, ink-jet process, as indicated in  FIG. 4  where the shape of the antenna  204 ,  205 , can be directly controlled by means of a computer during metal paste deposition. Any shape of the printed antenna  204 ,  205  can be obtained via this maskless ink-jet printing process. Without limiting the generality of the types of antennas,  FIGS. 2-3  demonstrate an example of the layout of the meander-like antenna  204 ,  205 , which is deposited on the plastic substrate  206 . Note that antenna  204 ,  205  can be implemented as a folded dipole, patch, spiral or loop antenna, depending upon design considerations. Note that system  400  can be utilized in such a manner that an impedance matching circuit and its layout are ink-jetted on the antenna substrate  206 .  
         [0026]     The concepts illustrated in  FIGS. 1-4  relate to the fabrication of an antenna plastic chip that can be provided with a hole or gap  202  formed in the region where the future cover  112  of the quartz sensor  100  will be accommodated. This allows for a good contact between the various sensor parts, which are placed in contact by flip chip technology and can thus reduce the height of the packaged device or system  300 . This substrate  206  can be, for example, Kapton®, or any plastic material with a glass transition temperature higher than 170° C. degrees. Note that Kapton® is a polyimide film developed by the DuPont Corporation which can remain stable in a wide range of temperatures, from −269° C. to 400° C. Kapton® is used in, among other things, flexible printed circuits and spacesuits. As an alternative to ink-jet deposition of the metal paste for the fabrication of antenna  204 ,  205 , the screen-printed technology can be used to obtain the desired layout of the antenna  204 ,  205 .  
         [0027]      FIG. 4  illustrates a perspective view of a maskless inkjet deposition printing system  400  that can be adapted for use in accordance with an embodiment. Note that system  400  depicted in  FIG. 4 , generally includes a unit  402  that is connected to tubes  404 ,  406  and  408 . Gas flow into component  402  occurs via tube  404 , while deposition material is provided through tube  406 . Atomized material  412  exits unit  402  via tube  408  and then enters an ink-jet print head  410  having a nozzle  411 . Gas  416  can be expelled from the nozzle  411  via a tube  414 . Ink jet printing of the antenna  204 ,  205  occurs on substrate  206  as described earlier.  
         [0028]     The novelty of the solution illustrated in  FIGS. 1-4  lies in the fact that the limited height of the resulting packaged wireless sensor or system  300  can be obtained by fitting the quartz cover  112  within the hole  202  configured in the plastic substrate  206 . The distance between the bond pads measured on the sensor chip being equal to the distance between the bond pads of antenna  204 ,  205  measured on the antenna chip will allow a good alignment and a reliable electrical connection of the sensor  100  and antenna  204 ,  205 . This principle can be applied to any type of antenna printed on the plastic substrate  206 . For the case of glass frit technology utilized to bond the two parts of the SAW sensor, the sum of thicknesses of the plastic substrate  206  and the height of the bumps  114  and  120  located on plastic substrate should be equal to the sum of the thickness of quartz cover  122  and the glass frit spacer height  122  and  128 . Such a configuration can create a planar surface on the backside of the resulting package or system  300 . The two bumps  114 ,  120 , of the meandering antenna  204 ,  205  represent the areas where the flip chip technology is applied to make an electrical connection respectively between the electrodes  126 ,  128  of sensor  100  and the ends  114 ,  120  of the antenna  204 ,  205 .  
         [0029]     The configuration depicted in  FIGS. 1-4  thus generally describes a new concept of final packaging for wireless SAW quartz sensors. The concept can be used for chip packaging of any wireless sensor, wherein an antenna cannot be integrated on the chip itself. As an example, the embodiments described herein are intended to solve the problem of a robust technology for chip level packaging and antenna and impedance matching circuit fabrication on a flexible substrate needed by a wireless pressure sensor cured in, for example, rubber. An innovative solution for chip packaging specific to “cured in the rubber pressure sensor” with potential low cost is therefore described herein.  
         [0030]     It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.