Abstract:
A manufacturing process of a semiconductor piezoresistive accelerometer includes the steps of: providing a wafer of semiconductor material; providing a membrane in the wafer over a cavity; rigidly coupling an inertial mass to the membrane; and providing, in the wafer, piezoresistive transduction elements, that are sensitive to strains of the membrane and generate corresponding electrical signals. The step of coupling is carried out by forming the inertial mass on top of a surface of the membrane opposite to the cavity. The accelerometer is advantageously used in a device for monitoring the pressure of a tire of a vehicle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a process for manufacturing a triaxial piezoresistive accelerometer and the relative pressure-monitoring device, in particular a device for monitoring the pressure of the tires of a motor vehicle, to which the ensuing description will make explicit reference, without any loss of generality.  
         [0003]     2. Description of the Related Art  
         [0004]     As known, in the automotive field there is an increasing use of devices for monitoring the pressure of tires (generally known as tire-pressure monitoring systems—TPMSs), which are designed to supply a timely communication, to the electronic control unit of the vehicle, of any fault or deviation with respect to the correct values of operation. These monitoring devices generally comprise a pressure sensor installed on the inner surface of the tire and designed to monitor its state of inflation; an appropriate electronic circuit, which reads the data provided by the pressure sensor and communicates with the electronic control unit (generally using radio-frequencies); and a wake-up system, which supplies a start-of-measurement signal to the pressure sensor and a data-collection signal to the electronic circuit connected thereto. In particular, the wake-up system makes it possible to limit the monitoring operation to the time intervals when the vehicle is moving (it is estimated that the average time of effective use of a vehicle is around 5% of the total life of the vehicle), and thus to reduce the energy consumption by the vehicle battery. Known wake-up systems are either of a mechanical type, generally formed by a mass coupled to a spring, or, as in the case of more recent systems, of an electronic type. Wake-up systems of an electronic type comprise an accelerometer arranged so as to detect the centrifugal acceleration of the tire as it turns. An acceleration of intensity higher than a preset threshold indicates a movement condition of the vehicle.  
         [0005]     The various components of the device for monitoring pressure are currently made using different technologies and subsequently assembled on an electronic board. The device is then coated with resin and individually packaged. Consequently, the pressure-monitoring device is currently cumbersome (around 10 mm in size) and somewhat complex to produce.  
         [0006]     Recently, the use has been proposed, within the pressure-monitoring device, of semiconductor piezoresistive accelerometers made using microfabrication techniques.  
         [0007]     As is known, piezoresistive sensors base their operation on piezoresistivity, i.e., the capacity of certain materials to modify their resistivity as the mechanical stresses acting on them vary. In detail, the resistivity decreases when compressive stresses are applied, whereas it increases when tensile stresses are applied.  
         [0008]     Semiconductor piezoresistive accelerometers generally comprise a membrane (or diaphragm) suspended over a cavity, and an inertial mass fixed to the membrane, and mobile with one or more degrees of freedom after detecting an acceleration. Piezoresistive elements (generally formed by implanted or diffused regions) are made in the surface region of the membrane and are connected to one another in a Wheatstone-bridge configuration. A deformation of the membrane, caused by the displacement of the inertial mass induced by the acceleration, causes an unbalancing of the Wheatstone bridge, which can be detected by a purposely provided electronic circuit, which derives, from said unbalancing, the desired measurement of acceleration.  
         [0009]     A triaxial piezoresistive accelerometer of a known type is, for example, manufactured by Fujikura Ltd. and described in detail in “www.sensorsmag.com/articles/0299/0299 — 38/main.shtml”.  
         [0010]     This accelerometer is illustrated in  FIG. 1 , where it is designated as a whole by reference number  1 . The accelerometer  1  comprises a first and a second silicon layer  2 ,  3 , between which glass layer  4  is arranged. In particular, the layers are bonded to one another via anodic bonding, and the entire structure is enclosed in a ceramic package (not illustrated in  FIG. 1 ).  
         [0011]     In extreme synthesis, the manufacturing process of the accelerometer  1  envisages the diffusion of boron regions in the surface region of the first silicon layer  2  so as to form piezoresistive elements  6  that are connected in a Wheatstone-bridge configuration (not illustrated in  FIG. 1 ). Then, the rear face of the first silicon layer  1  is anisotropically etched so as to form a thin silicon membrane  8 . After the etch, a central portion  9  of the first silicon layer  2  remains underneath the membrane  8 . Next, the glass layer  4  is bonded to the rear surface of the first silicon layer  2  via anodic bonding and the layer of glass  4  is cut on the rear side (opposite to the bonding side), so as to form an inertial mass  10  at the center of the structure of the accelerometer  1 , underneath the membrane  8 . In particular, the inertial mass  10  is etched only at the central portion  9 . Finally, the second silicon layer  3  is bonded via anodic bonding underneath the layer of glass  4 , which has the function of base and of mechanical protection for the accelerometer  1 . At the inertial mass  10 , the second silicon layer  3  has a cavity  12 , appropriately made before bonding, so as to ensure freedom of movement to the inertial mass  10 . The distance between the inertial mass  10  and the second silicon layer  3  is such as to limit the movement of the inertial mass  10  in a transverse direction, to prevent the membrane  8  from getting damaged in case of excessive accelerations.  
         [0012]     An acceleration imparted upon the accelerometer  1  causes a displacement of the inertial mass  10 , and a consequent deformation of the membrane  8 . Due to this deformation, the piezoresistive elements  6  vary their resistivity, so unbalancing the Wheatstone bridge.  
         [0013]     The accelerometer  1  described, even though it is certainly more compact than wake-up systems of a mechanical type, has in any case large dimensions on account of the need to carry out a bonding of three different layers (two layers of silicon and one layer of glass) and on account of the presence of a ceramic package, and entails a manufacturing process that is somewhat complex and costly. Furthermore, the accelerometer  1  cannot be readily integrated with the electronic read circuit. These disadvantages are particularly evident as regards the considered automotive applications, wherein low cost and simplicity of production are a constraint in the choice of the components to be used.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     One embodiment of the present invention provides an accelerometer overcoming the aforesaid disadvantages and problems, and in particular simple and inexpensive to manufacture, and simple to integrate within a pressure-monitoring device, in particular for automotive applications.  
         [0015]     According to the present invention, there are consequently provided a process for manufacturing an accelerometer as defined in claim  1 , and an accelerometer as defined in claim  9 .  
         [0016]     According to the present invention, a pressure-monitoring device is moreover provided, as defined in claim  15 . 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0017]     For a better understanding of the present invention, a preferred embodiment thereof is now described, purely by way of non-limiting example and with reference to the attached plate of drawings, wherein:  
         [0018]      FIG. 1  shows a cross-section of a piezoresistive accelerometer according to a known technique;  
         [0019]      FIG. 2  shows a top plan view of a wafer of semiconductor material in an initial step of a process of manufacturing an accelerometer according to the present invention;  
         [0020]      FIGS. 3-7  are cross-sections through the wafer of  FIG. 2  in subsequent steps of the manufacturing process according to the present invention;  
         [0021]      FIG. 8  shows a top plan view of the wafer of  FIG. 7 ;  
         [0022]      FIGS. 9   a - 10   a  are schematic representations of a portion of the wafer of  FIG. 7 , when subjected to accelerations;  
         [0023]      FIGS. 9   b - 10   b  show the bridge configuration of piezoresistive elements of the wafer of  FIG. 7 ;  
         [0024]      FIG. 11  shows a diagram corresponding to the distribution of the strains acting on a membrane portion of the wafer of  FIG. 7  when this is subjected to accelerations;  
         [0025]      FIGS. 12   a  and  12   b  are tables of sensitivity values of the accelerometer according to the present invention;  
         [0026]      FIG. 13  shows a block diagram of a pressure-monitoring device according to the present invention;  
         [0027]      FIG. 14  is a cross-section through a wafer of semiconductor material accommodating a pressure-monitoring device according to a first embodiment of the present invention; and  
         [0028]      FIG. 15  shows a second embodiment of the pressure-monitoring device of  FIG. 14 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     Hereinafter an embodiment is described of a manufacturing process of a triaxial piezoresistive accelerometer of semiconductor material. The manufacturing process is based upon the process described in EP-A-1 324 382, for manufacturing a SOI wafer, and on the process described in European patent application No. 04 425 197.3 filed in the name of the present applicant on 19 Mar. 2004, for manufacturing a pressure sensor.  
         [0030]      FIG. 2  shows a wafer  11  of semiconductor material, for example monocrystalline silicon, comprising a substrate  12 , for example of N type.  
         [0031]     In an initial step of the manufacturing process, a resist mask  13  is made on the wafer  11  (reference may also be made to the cross-section of  FIG. 3 ). In detail, the mask  13  has an approximately square area  14  comprising a plurality of hexagonal mask portions  13   a  that define a honeycomb lattice (as visible in the enlarged detail of  FIG. 2 ). For example, the distance t between opposite sides of the mask portions  13   a  is 2 μm, while the distance d between facing sides of adjacent mask portions  13   a  is 1 μm.  
         [0032]     Next (reference is made to  FIG. 4 ), using the mask  13 , the substrate  12  is anisotropically etched, thereby forming trenches  16 , having for example a depth of 10 μm, which communicate with one another and delimit a plurality of columns  17  of silicon. In practice, the trenches  16  form an open region  18  of a complex shape (corresponding to the honeycomb lattice of the mask  13 ) accommodating the columns  17  (with the same as the mask portions  13   a ).  
         [0033]     Next ( FIG. 5 ), the mask  13  is removed and an epitaxial growth is performed in a de-oxidizing environment (typically, in an atmosphere with a high concentration of hydrogen, preferably with trichlorosilane—SiHCl 3 ). Consequently, an epitaxial layer  20 , for example of an N type and having a thickness of 9 μm, grows on top of the columns  17  and closes the open region  18  at the top. The epitaxial layer  20  is shown only in  FIG. 5  and thereafter not distinguished from the substrate  12 .  
         [0034]     A thermal annealing is then performed, for example for 30 minutes at 1190° C., preferably in a hydrogen atmosphere, or alternatively a nitrogen atmosphere.  
         [0035]     As discussed in the aforementioned patent applications, the annealing causes a migration of the silicon atoms, which tend to move into the lower energy position. Consequently, and also thanks to the small distance between the columns  17 , the silicon atoms migrate completely from the portions of the columns  17  within the open region  18 , and a buried cavity  22  is formed, having a side of for example 500 μm. A thin silicon layer remains on top of the buried cavity  22  and forms a membrane  23 , that is formed in part by epitaxially grown silicon atoms and in part by migrated silicon atoms. The membrane  23  is flexible and can undergo deflection in presence of external stresses.  
         [0036]     Next ( FIG. 6 ), piezoresistive elements  24  are formed in a surface portion of the membrane  23  opposite to the cavity  22 . In detail, the piezoresistive elements  24  are obtained by diffusion or implantation of P type, for example of boron atoms, and are connected to one another in a Wheatstone-bridge configuration, as will be explained in detail hereinafter. In  FIG. 6 , the interconnections  26  between the piezoresistive elements  24  (typically formed by metal regions extending on an insulating layer, not illustrated) are represented in a schematic way. Furthermore, as an alternative to what is illustrated, the piezoresistive elements  24  can be made of polysilicon on top of the membrane  23 .  
         [0037]     Next ( FIG. 7 ), according to one aspect of the present invention, on top of the membrane  23  an inertial mass  25  is deposited, using a silk-screen printing technique, and is formed by welding paste, for example of silver, tin, copper, lead, gold, or of other high-density metals (preferably having a density higher than 7000 kg/m 3 ). For example, the welding paste is commonly used in the fabrication of packages of electronic components.  
         [0038]     In detail, the inertial mass  25  is deposited approximately at the geometrical center of the membrane  23  through a metal mesh (not illustrated), for example of nickel or steel, which has suitable openings at the deposition areas of the welding paste.  
         [0039]     Deposition is accompanied by an increase in temperature, during which the inertial mass  25  adheres to the top surface of the membrane  23 . After cooling, the shape of the inertial mass  25  (as illustrated in  FIG. 7  and in the top plan view of  FIG. 8 ) comprises a cylindrical base portion and a hemispherical top portion. In particular, the inertial mass  25  has a height such that its centroid G is located outside of the membrane  23 . The shape of the inertial mass  25  is given not only by the size of the openings of the metal mesh used for its deposition, but also by the surface tensile stresses created between the inertial mass  25  and the membrane  23 , and by the resting base of the inertial mass  25  on the membrane  23 .  
         [0040]     Next, a covering region  28 , for example of semiconductor material or glass, can possibly be bonded via anodic bonding to the top surface of the wafer  11 , for ensuring a mechanical protection for the sensing structure. In particular, the covering region  28  has a cavity  29  at the membrane  23 , so as to not alter the freedom of movement.  
         [0041]      FIG. 8  shows a top plan view of the wafer  11 , highlighting the arrangement of the piezoresistive elements  24  with respect to the inertial mass  25 . The axes x, y and z of a Cartesian reference system associated to the wafer  11  are also shown in  FIG. 8 . In particular, the top surface of the wafer  11  lies in the plane xy.  
         [0042]     In detail, the piezoresistive elements  24  are arranged to form a cross along the axes x and y, and the inertial mass  25  is located at the center thereof. Each arm of the cross is formed by two groups of four piezoresistive elements  24  aligned and connected to one another in a Wheatstone-bridge configuration. As will be described in detail hereinafter, the piezoresistive elements  24 , designated by R 1x -R 4x , refer to the detection of an acceleration along the axis x, the ones designated by R 1y -R 4y  refer to the detection of an acceleration along the axis y, and the ones designated by R 1z -R 4z  and R 1z ′-R 4z ′ refer to the detection of an acceleration along the axis z. Consequently there are present a Wheatstone bridge for detecting an acceleration along the axis x and the axis y, and two Wheatstone bridges connected in common mode for detecting an acceleration along the axis z.  
         [0043]     Operation of the above triaxial accelerometer is described hereinafter (see  FIGS. 9 and 10 ).  
         [0044]     Since the centroid G of the inertial mass  25  is located outside of the membrane  23 , an acceleration directed along the axis x or the axis y acting on the accelerometer brings about a momentum on the inertial mass  25 , which causes inclination thereof in the corresponding direction (as illustrated in  FIG. 9   a ). The displacement of the inertial mass  25  brings about a corresponding deformation of the membrane  23  and a variation in the resistivity of the piezoresistive elements  24  arranged along the direction of the acceleration. In particular, the piezoresistive elements R 1x /R 1y  and R 3x /R 3y  undergo a tensile stress, which increases their own resistivity, while the piezoresistive elements R 2x /R 2y  and R 4x /R 4y  undergo a compressive stress, which decreases their own resistivity. As illustrated in  FIG. 9   b , the piezoresistive elements  24  referred to above are arranged in a Wheatstone-bridge configuration so as to increase the sensitivity of the bridge, i.e., elements with resistivities which undergo opposite variations are arranged in adjacent arms of the bridge.  
         [0045]     Likewise, an acceleration directed along the axis z acting on the accelerometer causes a corresponding displacement of the inertial mass  25  and a consequent deformation of the membrane  23 , as illustrated in  FIG. 10   a . In this case, the piezoresistive elements R 1z  and R 4z  undergo a tensile stress, that increases their own resistivity, while the piezoresistive elements R 2z  and R 3z  undergo a compressive stress, that decreases their own resistivity.  FIG. 10   b  shows the corresponding arrangement in a Wheatstone-bridge configuration of the piezoresistive elements  24  mentioned above.  
         [0046]     It should be noted that, since the buried cavity  22  has a thickness of a few microns, the possibility of deflection of the membrane in the direction of the axis z is limited. In this way, a mechanical constraint is created that limits the amplitude of the displacements along the axis z, to prevent any possible failure of the accelerometer.  
         [0047]      FIG. 11  shows the distribution of the stresses acting on the membrane  23  upon application of an acceleration of 5 g along the axis z. As may be noted, the intensity of the compressive stress has a maximum value in the neighborhood of the inertial mass  25  (represented as a spheroid in  FIG. 11 ), while the intensity of the tensile stress is maximum at the peripheral edges of the membrane  23 . The piezoresistive elements R 1z -R 4z  are consequently formed at the regions of the membrane  23  that are subjected to the stresses of maximum intensity. Similar considerations apply to the piezoresistive elements  24  corresponding to the axes x and y.  
         [0048]     In a per se known and not illustrated manner, the unbalancing of the Wheatstone bridge is then detected by an appropriate electronic circuit, generally comprising an instrumentation amplifier, which receives the unbalancing voltage V out  of the Wheatstone bridge; the desired information of acceleration is then derived from the unbalancing.  
         [0049]     The sensitivity Sens of the accelerometer is directly affected by the dimensions of the inertial mass  25 . In particular, the sensitivity Sens increases as the inertial mass  25  increases, in so far as the consequent deformation of the membrane  23  increases, but only up to a certain limit, beyond which the dimensions of the inertial mass  25  become such as to stiffen the membrane  23  excessively and to limit its freedom of movement.  
         [0050]     The tables of  FIGS. 12   a  and  12   b  illustrate the value of the sensitivity Sens of the accelerometer as the radius of the inertial mass  25  (again shown as a spheroid) varies, respectively for an acceleration acting in the plane xy and for an acceleration acting in the direction z. The value of sensitivity is normalized with an acceleration of 5 g and a voltage of 5 V, and is expressed in μV/g/V. The tables give moreover the values, expressed in Pa, of the longitudinal stresses S l  and of the transverse stresses S t  (corresponding to the position of the piezoresistive elements  24  in the plane xy) to which the membrane  23  is subjected.  
         [0051]     From the tests conducted by the applicant, it emerges that, in order to obtain a higher sensitivity Sens of the accelerometer, it is convenient to use inertial masses  25  having a radius of between 100 μm and 200 μm. With reference to the dimensions of the membrane  23  (the side whereof is approximately 500 μm), the accelerometer is found to have a higher sensitivity when the ratio between the radius of the inertial mass  25  and the side of the membrane  23  is between 20% and 40% (or, likewise, the ratio between the diameter of the inertial mass  25  and the side of the membrane  23  is between 40% and 80%). Furthermore, it emerges that the sensitivity of the accelerometer is higher along the axis z than along the axes x and y.  
         [0052]     The accelerometer described can be used in a device for monitoring the inflation pressure of the tires of a vehicle.  
         [0053]     In detail, as illustrated in  FIG. 13 , a pressure-monitoring device  30  comprises an accelerometer  35 , made as described previously and designed to detect the centrifugal acceleration of a tire (not illustrated); a pressure sensor  36 , of piezoresistive type, connected to the accelerometer  35  and designed to measure the pressure of inflation of the tire; and an electronic circuit  37 , connected to the accelerometer  35  and to the pressure sensor  36  and communicating with the electronic control unit of the motor vehicle (not shown), for example via radio-frequencies. In particular, the pressure-monitoring device  30  is arranged at the inner surface of the tire, so that the accelerometer  35   b  detects the centrifugal acceleration along the axis z due to the rotation of the tire.  
         [0054]     The technology used for manufacturing the accelerometer  35  is substantially similar to the one used for the pressure sensor  36  (see in this regard the aforementioned European patent application No. 04 425 197.3). Consequently, integration of the pressure sensor and of the accelerometer according to the present invention in a same substrate of semiconductor material proves simple and economically advantageous. Furthermore, also the electronic circuit  37  can be readily integrated in the same substrate, rendering the pressure-monitoring device  30  extremely compact and simple and fast to produce.  
         [0055]      FIG. 14  shows the pressure-monitoring device  30  integrated in a wafer  31  of semiconductor material, for example of monocrystalline silicon, which comprises a substrate  32 , for example of an N type.  
         [0056]     Within the wafer  31  three regions may be distinguished: a first region  34   a , accommodating an accelerometer  35  made as described with reference to FIGS.  2  to  7  (so that parts that are similar are designated by the same reference numbers); a second region  34   b , accommodating a piezoresistive pressure sensor  36 ; and a third region  34   c , accommodating an electronic circuit  37 .  
         [0057]     In detail, the pressure sensor  36  comprises a buried cavity  40 , a membrane  41 , and piezoresistive elements  42  diffused or implanted within the membrane  41 . Advantageously, a fair number of the manufacturing process of the pressure sensor  36  and of the accelerometer  35  are in common (for example, forming the trenches, annealing, depositing the piezoresistive elements, etc.).  
         [0058]     The electronic control circuit  37  ( FIG. 14  shows only by way of example an NPN transistor comprising a collector region  45  of an N type, a base region  46  of a P type, and an emitter region  47  of an N type) is also made using manufacturing steps in common with the process of the accelerometer  35  and of the pressure sensor  36 . For example, the diffusion of the base region  46  is performed simultaneously with the diffusion of the piezoresistive elements. In a way not illustrated in  FIG. 14 , electrical-insulation regions can be envisaged for insulating electrically the electronic control circuit  37  from the second region  34   b.    
         [0059]     At the end of the manufacturing process, after depositing the inertial mass  25  of the accelerometer  35 , appropriate electrical-contact regions  50  (illustrated schematically) are made for the electrical connection of the accelerometer  35 , of the pressure sensor  36 , and of the electronic control circuit  37 . Further electrical-contact regions are provided for the electrical connection of the electronic circuit  37  with the outside world (in particular with the electronic control unit of the vehicle, not illustrated herein).  
         [0060]     The wafer  31  can then be encapsulated in a package  51  (illustrated schematically in  FIG. 14 ) so that only the membrane  41  of the pressure sensor  36  is accessible from the outside, while the remaining components are mechanically protected.  
         [0061]     The above triaxial piezoresistive accelerometer and the pressure-monitoring device have the following advantages.  
         [0062]     In particular, the accelerometer has extremely reduced dimensions, since it is integrated in a single substrate and does not need bonding of wafers of different materials. Furthermore, the fabrication of the inertial mass using welding paste of high-density metals enables, for a same sensitivity, to reduce the dimensions of the inertial mass as compared to when other materials having a lower density (for example silicon) are used. The manufacturing process is extremely simple and inexpensive, and furthermore, the particular construction is compatible with packaging techniques at the substrate level, such as the bump-bonding or flip-chip techniques, which enable a further reduction in the dimensions. Furthermore, the sensitive part of the sensor is automatically and mechanically protected on the back of the wafer because of the presence of the buried cavity within the substrate.  
         [0063]     The pressure-monitoring device is, in turn, extremely compact, thanks to the integration of all the components, including the electronic control circuit, in a single body of semiconductor material. In this way, it is possible to reach dimensions smaller than 1 mm. Furthermore, the manufacturing process is simpler and faster, since process steps for obtaining the various components of the device are in common. The resulting chip can also be connected with flip-chip techniques.  
         [0064]     Finally, it is clear that modifications and variations can be made to the process and device described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the annexed claims.  
         [0065]     In particular (see  FIG. 15 ), a second embodiment of the pressure-monitoring device  30  provides for forming the accelerometer  35  on the back of the wafer  31 , so as to obtain a further reduction of the occupied area. In detail, the manufacturing process according to the second embodiment comprises first forming the pressure sensor  36  in a front surface portion of the wafer  31 . Then, after coating the top surface of the wafer  31  with a sheet of protective material, the wafer  31  is turned upside down (this is possible given the planarity of the pressure sensor  36  and the absence of any projecting portions), so as to obtain the accelerometer  35  on the back of the wafer  31 . In particular, the annealing steps can advantageously be made simultaneously for both of the sensors.  
         [0066]     In addition, the geometrical shape of the membrane can be different, for example can be circular or generically polygonal; also the shape of the inertial mass can differ from the one described and can be, for example, cylindrical.  
         [0067]     The shape of the columns  17  can vary with respect to the one illustrated; for example the columns  17  can be replaced by diaphragms of semiconductor material of small thickness, or in general by other thin structures (walls) such as to enable migration of silicon during the annealing step and formation of the deep cavity  22 .  
         [0068]     Furthermore, it is clear that the described accelerometer can advantageously be used in other applications, in particular in all those applications that require reduced overall dimensions and costs. For example, it can be used in a wake-up system of a portable device, or for detection of a free fall of the portable device.  
         [0069]     Finally, the described pressure-monitoring device can be used for other applications. For example, in the automotive field, it can be used for monitoring the pressure of the air-bag, for controlling the breakdown pressure of the ABS, and for monitoring the pressure of the oil or the pressure of fuel injection.  
         [0070]     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.