Patent Publication Number: US-2009217760-A1

Title: Sensing apparatus

Description:
This application is a divisional application of Ser. No. 11/263,834, filed on Nov. 2, 2005, which is a Non-provisional application which claims priority under U.S.C.§ 119(a) on Patent Application No(s). 093140886 filed in Taiwan, Republic of China on Dec. 28, 2004, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates to a sensing apparatus, and more specifically to a sensing apparatus utilizing film bulk acoustic resonators (FBARs). 
     With the growth of the biotechnology, biomedical gauges have been scaled down from conventional large-sized apparatuses to small portable home-based devices capable of fast operation. In addition, in terms of mechanical industries such as an automobile industry, conventional mechanical apparatuses have evolved into sophisticated fine-tuned systems including a plurality of sensors to improve integration of automobiles with comfort and security features for drivers and passengers. All these applications, however, require sophisticated and real-time sensors. 
     Surface acoustical wave (SAW) devices are not only used widely in communications but also in sensors. Fast and highly accurate measurement can be obtained by measuring the variation of real-time SAW devices with high sensitivity. Conventional SAW devices made of piezoelectric materials which are single crystal or bulk are characterized in their piezoelectric characteristics, they are, however, costly. Additionally, because of limitations in materials and manufacturing processes, the higher the operating frequency, the greater the energy attenuation. Consequently, SAW devices are not capable of operating in high frequency. 
     Moreover, conventional SAW devices require additional fabrication to be integrated into ordinary semiconductor components. Hence, the overall size is not reduced and the production cost and time are increased. Further, possible variations in characteristics of SAW devices also increase due to additional fabrication processes. 
     SUMMARY 
     In view of the above, the present invention provides a sensing apparatus utilizing film bulk acoustic resonators (FBARs) with fast and highly accurate measurement characteristics and advantages such as small size, low production cost, low power consumption and being suitable for use in high operating frequency. Moreover, FBARs can be integrated with conventional semiconductor components into one single chip in a wafer manufacturing stage, whereby avoiding additional fabrication processes and variations in characteristics caused thereby. 
     According to one aspect of the invention, the sensing apparatus for measuring a force includes a film bulk acoustic resonator (FBAR) having a bulk acoustic wave velocity (Vb) and a corresponding resonant frequency (f). When the FBAR is subjected to the force, the bulk acoustic wave velocity and the resonant frequency change to obtain a frequency downshift (Δf) in response to deformation caused by the force, and a magnitude of the force is obtained by calculating the frequency downshift (Δf). The FBAR includes a pair of electrodes and a piezoelectric layer sandwiched therebetween. When a high-frequency voltage signal is inputted to one of the electrodes, a bulk acoustic wave having the Vb and the resonant frequency is formed and progresses between the electrodes. The high-frequency voltage signal is generated by an oscillating circuit which is electrically connected to one of the electrodes or a wireless transmitter whereas the high-frequency voltage signal is received by an antenna which is electrically connected to one of the electrodes. The antenna generates a signal corresponding to the frequency downshift (Δf) and transmits the signal to the wireless transmitter for calculating the magnitude of the force. 
     The force is acceleration, g-force or air pressure. The sensing apparatus is electrically connected to a frequency counter for obtaining the frequency downshift (Δf). There is an oscillator or an amplifier coupled between the sensing apparatus and the frequency counter for modulating the frequency downshift (Δf). The sensing apparatus is integrated into a semi-conductor chip in the wafer manufacturing stage and is manufactured by Microelectromechanical (MEMS) technology. 
     According to another aspect of the invention, a sensing apparatus includes an impedance sensor, a film bulk acoustic resonator (FBAR) electrically connected to the impedance sensor, and a matching circuit for adjusting the impedance between the FBAR and the impedance sensor, wherein the sensitivity of the impedance sensor is increased by a high operating frequency of the FBAR. The impedance sensor is operative to measure an air pressure, such as the tire pressure of a motor vehicle, or measure an acceleration caused by the torsion of a spinning object. 
     The FBAR includes a pair of electrodes and a piezoelectric layer sandwiched therebetween. When a high-frequency voltage signal is inputted to one of the electrodes, a bulk acoustic wave having the Vb and the resonant frequency is formed to progress between the electrodes. Alternatively, the FBAR includes at least two piezoelectric layers and a plurality of electrodes for providing more variations of the FBAR connection. The piezoelectric layer is made of AlN, ZnO, PZT or BaTiO 3 . Further, the impedance sensor and the FBAR are integrated into a semi-conductor chip in the wafer manufacturing stage and the sensing apparatus is manufactured by Microelectromechanical (MEMS) technology. 
     According to another aspect of the invention, a sensing apparatus including a film bulk acoustic resonator (FBAR) having a bulk acoustic wave velocity (Vb) and a corresponding resonant frequency (f), and a chemical or biochemical sensitive substance disposed on the FBAR. If a tested object reacts with the chemical or biochemical sensitive substance, the weight of the chemical or biochemical sensitive substance is changed, and the force is generated. Thus, the chemical or biochemical characteristic of the tested object is obtained. 
     The FBAR includes a pair of electrodes and a piezoelectric layer sandwiched therebetween. When a high-frequency voltage signal is inputted to one of the electrodes, a bulk acoustic wave, having the Vb and the resonant frequency (F), is formed to progress between the electrodes. The high-frequency voltage signal is generated by an oscillating circuit which is electrically connected to one of the electrodes or a wireless transmitter whereas the high-frequency voltage signal is received by an antenna which is electrically connected to one of the electrodes. The antenna further generates and transmits a signal corresponding to the frequency downshift (Δf) to the wireless transmitter for obtaining the chemical or biochemical characteristics of the tested object. The piezoelectric layer is made of AlN, ZnO, PZT or BaTiO 3 . 
     The sensing apparatus is electrically connected to a frequency counter for obtaining the frequency downshift (Δf), wherein an oscillator or an amplifier is coupled between the sensing apparatus and the frequency counter for modulating the frequency downshift (Δf). The sensing apparatus is integrated into a semi-conductor chip in the wafer manufacturing stage and manufactured by Microelectromechanical(MEMS) technology. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
         FIG. 1A  is a schematic diagram of a thin film bulk acoustic resonator (FBAR) of the invention. 
         FIG. 1B  is a schematic diagram showing that the FBAR in  FIG. 1A  is subjected to a force. 
         FIG. 2A and 2B  are block diagrams of sensing apparatus according to the first embodiment of the invention. 
         FIG. 2C  is a block diagram showing the sensing apparatus with a wireless transmitter according to the first embodiment of the invention. 
         FIG. 3A  is a schematic diagram of a sensing apparatus according to the second embodiment of the invention. 
         FIG. 3B  is a schematic diagram of another sensing apparatus according to the second embodiment of the invention. 
         FIG. 4  is a schematic diagram of an embodiment of a thin film bulk acoustic resonator (FBAR) with a chemical or biochemical sensitive substance according to the invention. 
     
    
    
     DETAILED DESCRIPTION  
     The invention provides a sensing apparatus utilizing FBARs which have advantages such as low production cost, power consumption and being suitable for use in high operating frequency (up to 10 GHz) in order to improve the testing characteristics of the sensing apparatus. The operation of FBARs is described in the following. 
       FIG. 1A  is a FBAR according to an embodiment of the invention. The FBAR  12  includes a pair of electrodes  13   a  and  13   b,  and a piezoelectric layer  14  sandwiched between the electrodes  13   a  and  13   b.  The FBAR  12  is formed on a substrate  11  having deformation capability and, the electrode  13   a  is electrically connected to an oscillating circuit  79 . 
     When the oscillating circuit  79  generates a high-frequency voltage signal to the FBAR  12  via the electrode  13   a,  a bulk acoustic wave is excited because of the piezoelectric effect to progress between the upper electrode  13   a  and lower electrode  13   b.  Because of the boundary reflection, the transmission of the acoustic wave becomes a standing wave resonance, wherein an equation relating to the resonant frequency, the bulk acoustic wave velocity, and the piezoelectric thin film thickness thereof is as follows. 
         F=Vb /(2* t ); 
     wherein f is the resonant frequency, Vb is the bulk acoustic wave velocity and t is the thickness of the piezoelectric layer  14 . 
     Thus, when one of the electrodes of the FBAR  12  receives a high-frequency voltage signal, a bulk wave is generated to progress between electrodes  13   a  and  13   b.  As the results, a bulk acoustic wave velocity (Vb) and a corresponding resonant frequency (f) of the bulk wave are abtained. 
       FIG. 1B  shows that the FBAR of  FIG. 1A  is subjected to a force. When the pressure of A is greater than that of B, the FBAR  12  is deformed due to the force, as shown in  FIG. 1B . Because of the deformation of the FBAR  12 , the bulk acoustic wave velocity (Vb) changes and the resonant frequency (f) changes accordingly. Therefore, the magnitude of the pressure of A can be then obtained by calculating the frequency downshift (Δf). 
     In addition, the FBAR is deformed because of not only uneven surrounding air pressure but also acceleration or g-force. In order to enable those skilled in the art to practice the invention, embodiments according to the invention with the described principle of the FBAR are described in the following. 
     FIRST EMBODIMENT 
       FIGS. 2A and 2B  are schematic diagrams of a sensing apparatus according to the first embodiment of the invention. The sensing apparatus  20  according to the first embodiment of the invention includes a FBAR  22  coupled to an oscillating circuit for receiving a high-frequency voltage signal. The sensing apparatus  20  is further electrically connected to a frequency counter  27 . Also, there is further an oscillator  25  (as shown in  FIG. 2A ) or an amplifier  26  (as shown in  FIG. 2B ) coupled between the sensing apparatus  20  and the frequency counter  27 . 
     The FBAR  22  has a bulk acoustic wave velocity (Vb) and a corresponding resonant frequency (f). When the FBAR  20  is subjected to a force, FBAR  12  is deformed, and the bulk acoustic wave velocity (Vb) changes, and then the resonant frequency (f) changes accordingly. After modulation of the oscillator  25  or the amplifier  26 , the magnitude of the force can be obtained by calculating the frequency downshift (Δf) by using the frequency counter  27 . 
     Additionally, the high-frequency voltage signal can be provided to the FBAR  22  either by wired or wireless transmission. Referring to  FIG. 2C , which is a block diagram showing a sensing apparatus with wireless transmitter according to the first embodiment of the invention. The sensing apparatus  20  receives the high-frequency voltage signal via an antenna and a feedback signal corresponding to Δf is generated thereby to a transmitter  89 . The high-frequency voltage signal is provided by the transmitter  89  and received via the antenna coupled to the electrodes of the FBAR  22 . 
     Moreover, the magnitude of the force can be obtained by calculating the signal corresponding to Δf received by the transmitter  89  by using the frequency counter  27 . 
     SECOND EMBODIMENT 
     The first embodiment utilizes the FBAR  22  to obtain the magnitude of the force, which can also be obtained by coupling the FBAR to an impedance sensor in parallel or in series. Because the resonant frequency changes in response to the input impendence of the impedance sensor, the force can be obtained by detecting the resonant frequency of the FBAR. Referring to  FIG. 3A , which shows a sensing apparatus according to the second embodiment of the invention. The sensing apparatus  30  includes an impedance sensor  38 , a FBAR  32   a,  and a matching circuit  39 . The FBAR  32   a  is electrically connected to the impedance sensor  38 , and the matching circuit  39  is used to adjust the impedance between the FBAR  32   a  and the impedance sensor  38 , wherein the matching circuit  39  also provides a better coupling effect between the FBAR  32   a  and the impedance sensor  38 . 
     The sensitivity of the impedance sensor  38 , such as a capacitance or resistive pressure sensor, can be improved by the high operating frequency of the FBAR  32   a.  Moreover, the impedance sensor  38  is capable of detecting an air pressure, such as the tire pressure of a motor vehicle or an acceleration caused by the torsion of a spinning object. 
     The FBAR  32   a,  which is similar to the FBAR  22  according to the first embodiment of the invention, includes a pair of electrodes and a piezoelectric layer sandwiched therebetween. When a high-frequency voltage signal is inputted to one of the electrodes, a bulk acoustic wave having a buck acoustic wave velocity (Vb) and the corresponding resonant frequency (f) is formed to progress between the electrodes. 
     Alternatively, a two-port FBAR can also be employed. Referring to  FIG. 3B , which shows another sensing apparatus according to the second embodiment of the invention. The FBAR  32   b  includes at least two piezoelectric layers and a plurality of electrodes. The FBAR  32   b  is electrically connected to the impedance sensor  38 , and the impedance between the FBAR  32   b  and the impedance sensor  38  is adjusted by the matching circuit  39 . The matching circuit  39  also provides a better coupling effect between the FBAR  32   b  and the impedance sensor  38 . 
     With reference to  FIG. 3B , the electrode of the lower piezoelectric layer in the FBAR  32   b,  having two piezoelectric layers, is electrically connected to the impedance sensor  38 , so that the impendence of the first port P of the FBAR  32   b  is changed, and the resonant frequency measured by the first port P is also changed accordingly. This provides more flexibility in connection of the FBAR. Thus, a best connection way regarding different impedance sensors can be adopted according to different impendence of the impedance sensors so as to achieve best measure sensitivity. 
     Both the FBARs  32   a  and  32   b  improve the sensitivity of the sensing apparatus  30  and the FBARs  32   a  and  32   b  can be integrated into a chip with impedance sensors manufactured by Microelectromechanical (MEMS) technology, such as Pressure Gauges, Accelerometers and the like, to reduce the production cost, simplify fabrication and achieve miniaturization. 
     THIRD EMBODIMENT 
     The first and second embodiments utilize the deformation characteristic of forced FBARs. The FBAR, however, can also be utilized for a chemical or biochemical sensors. The sensing apparatus of the third embodiment includes a FBAR and a chemical or biochemical sensitive substance  15  as shown in  FIG. 4 . The FBAR has a bulk acoustic wave velocity (Vb) and a corresponding resonant frequency (f). The chemical or biochemical sensitive substance is disposed on the FBAR by deposition, coating or other equivalent methods. If a tested object reacts with the sensitive substance, the tested object will combine with the sensitive substance, transform the sensitive substance, or make the sensitive substance to fall off, so that the weight of the sensitive substance is then changed, which consequently changes the loading on the surface of the FBAR. Thus, the bulk acoustic velocity (Vb) then changes, resulting in a shift of the resonant frequency (f), called a frequency downshift (Δf). Therefore, the chemical or biochemical characteristic of the tested object is obtained. Conversely, if the frequency downshift (Δf) is zero, it means the tested object does not have this chemical or biochemical characteristic. In addition, different chemical or biochemical sensitive substances can be coated on the surface of the FBAR according to different chemical or biochemical characteristics of the tested object. 
     Moreover, the sensing apparatus of the third embodiment can also utilize the wireless transmitter disclosed in the first embodiment to detect the resonant frequency of the FBAR. Because this is a passive detection which does not need additional power supply, disadvantages of active sensing apparatuses, such as limited battery life, and additional weight, size and production cost, are then eliminated. Moreover, using FBARs is also preferred for their advantages such as higher Q value than SAW devices&#39;, low power consumption and the same production cost but with higher operating frequency. Therefore, take a wireless passive sensor used in the 2.4 GHz ISM band as the example, a sensing apparatus with a FBAR is the first choice. 
     Further, the above-described sensing apparatuses can be manufactured by Microelectromechanical (MEMS) technology and the FBAR disposed on a silicon substrate can be integrated into a semiconductor chip in wafer manufacturing stage, avoiding additional fabrication and thus reducing production cost, simplifying the manufacturing process and achieving miniaturization. 
     In conclusion, the sensing apparatuses disclosed in the present invention utilizing a film bulk acoustic resonator (FBAR) manufactured with a piezoelectric thin film by MEMS technology. The sensing apparatuses have fast and highly accurate measurement characteristics and also have advantages such as small size, low production cost, low power consumption, and being suitable for use in high operating frequency (up to 10 GHz). Moreover, the FBAR can be integrated into one single chip with conventional semiconductor components, whereby reducing production cost, simplifying fabrication and achieving miniaturization. The variation of characteristics caused by additional processes is thus avoided. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.