Abstract:
Electrical devices having tunable electrical characteristics are provided, such as variable resistors, capacitors and inductors. The tunable electrical characteristics are achieved by placing an appropriate material between substrate layers and by controllably applying a pressure to the material to compress the material or alter the shape of a well in which the material is contained, and thereby alter the electrical characteristics of the electrical device. The composition, shape and dimension of the embedded materials determine how the electrical characteristics of the electrical device are altered upon compression of the embedded material in response to an applied control signal. Generally, as the embedded material is compressed, the material will become more dense and the electrical characteristics of the integrated electrical device is altered.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to integrated electronic components and, more particularly, to integrated electronic elements that provide adjustable electrical characteristics. 
   BACKGROUND OF THE INVENTION 
   The fabrication of electrical devices, such as resistors, capacitors, and inductors, in integrated devices is well known. Typically, integrated electrical devices are formed by embedding appropriate materials in a substrate. The resulting integrated electrical device typically has relatively fixed electrical characteristics. However, in many applications, the electrical characteristics of such devices must be varied, depending upon the requirements of the given application, including feedback from the output or other circuit requirements to vary the electrical characteristics. Thus, a number of techniques have been proposed or suggested for varying the electrical characteristics of integrated electrical devices in order to maintain the electrical characteristics within specified limits. U.S. Pat. No. 5,543,765, for example, discloses electronic elements having variable electrical characteristics. The electronic elements include a cavity in which a moving insulator element shifts. The moving insulator element is partially covered with an electrically conductive material. An electrical field shifts the moving element to thereby vary the electrical characteristics of the electronic element. 
   While such proposed techniques may provide a mechanism for maintaining electrical characteristics within a specified range, they often have power or surface area requirements (or both) that are not practical within the constraints of commercially viable integrated devices. A need therefore exists for improved techniques for varying the electrical characteristics of integrated electrical devices in both real time and/or with a feedback. mechanism 
   SUMMARY OF THE INVENTION 
   Generally, electrical devices having tunable electrical characteristics are provided, such as variable resistors, capacitors and inductors. The tunable electrical characteristics are achieved by placing an appropriate material between substrate layers and by controllably applying a pressure to the material to compress the material or alter the shape of a well in which the material is contained, and thereby alter the electrical characteristics of the electrical device. The composition, shape and dimension of the embedded materials determine how the electrical characteristics of the electrical device are altered upon compression of the embedded material in response to an applied control signal. Generally, as the embedded material is compressed, the material will become more dense and the electrical characteristics of the integrated electrical device are altered. 
   A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are schematic diagrams of an exemplary integrated resistive device having a tunable resistance value in accordance with the present invention in an uncompressed and compressed state, respectively; and 
       FIGS. 2A and 2B  are schematic diagrams of an exemplary integrated capacitive device having a tunable capacitance in accordance with the present invention in an uncompressed and compressed state, respectively. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A and 1B  are schematic diagrams of an exemplary integrated resistive device  100  having tunable electrical characteristics in accordance with the present invention in an uncompressed and compressed state, respectively. As shown in  FIG. 1A , the exemplary integrated resistive device  100  includes a material  110  embedded in a substrate  120 . According to one aspect of the invention, one or more pressure plates  150 - 1  and  150 - 2  are applied to the substrate  120  in order to compress the material  110  and thereby alter the resistance of the integrated device  100 . As discussed hereinafter, a pair of pressure plates  150  is applied to opposite sides of the substrate  120  in the exemplary embodiment. In a further variation, however, a fixed plate (or the substrate itself) can be used on one side of the substrate  120 , while a single pressure plate  150  is applied to the opposite side of the substrate  120  to compress the material  110 , as would be apparent to a person of ordinary skill in the art. It is noted that the applied pressure can be greater than or less than atmospheric pressure and can include a suction effect. 
   The pressure plates  150  will selectively compress the embedded material  110  upon application of an appropriate control signal  160  to the pressure plates  150 . The pressure plates  150  may be embodied, for example, as bimetallic plates, piezo electric plates or plates controlled by a micro-electrical mechanical system (MEMS). The pressure plates  150  are in one position when a first voltage is applied and in a second position when a second voltage is applied. In the exemplary embodiment shown in  FIGS. 1A and 1B , the bimetallic pressure plates  150  will bow upon application of an appropriate control signal  160 . In a further variation, a variable scale between the uncompressed and compressed states can be established by application of an appropriate control signal  160  that determines the degree of compression caused by the pressure plates  150 , in a known manner. Thus, the control signal  160  determines the extent to which the embedded material  110  is compressed, and the resulting degree to which the electrical characteristic is altered. The control signal  160  can also be supplied by a feedback loop in real time to make automatic adjustments based upon the signal and or circuit requirements. For example, for the integrated resistive device  100  shown in  FIGS. 1A and 1B , the control signal  160  determines the extent to which the embedded material  110  is compressed, and the resulting degree to which the resistance of the integrated resistive device  100  is altered. 
   According to one aspect of the present invention, the resistance of the integrated device  110  will vary depending on whether the integrated device  110  is in an uncompressed or compressed state, or an intermediate state in between. As shown in  FIGS. 1A and 1B , a signal passing between input and output terminals  170 - i  and  170 - o , respectively, through the embedded material  110  will incur a corresponding voltage drop across the integrated device  110  depending on whether the device  110  is in an uncompressed or compressed state. For example, the integrated device  110  may have a resistance value of 10 ohms in an uncompressed state and a resistance value of 100 ohms in a compressed state. 
   In yet another variation of the present invention, the compression applied by the pressure plates  150  may be done continuously or intermittently. A continuous compression will introduce a different change in the electrical characteristics of the integrated electrical device than the vibration effect caused by an intermittent pressure. The pressure plates  150  may thus be controlled by transducers or similar devices that allow the pressure plates  150  to vibrate at a desired frequency. The shape of cavity in which the material  110  is retained may also be selected to achieve different results. 
   As previously indicated, a material  110  is placed inside the layers of the substrate  120 . As a signal passes through the material  110 , a particular electrical characteristic of the integrated device is varied as the material is compressed. In one exemplary implementation of an integrated resistive device  100 , the material  110  may be a copper (Cu) paste or silver (Ag) paste. The resistance material can be mixed with Carbon (C) and a suspension compound to keep the finished material in a grease or gel state. The resistance value can be adjusted from 1 ohm up to 1 mega-ohm depending on the formulation. Generally, the material  110  is selected so that the response to the signal and the mechanical action is sufficient to produce the range of variation in the electrical characteristic which is required. 
     FIGS. 2A and 2B  are schematic diagrams of an exemplary integrated capacitive device  200  having tunable electrical characteristics in accordance with the present invention in an uncompressed and compressed state, respectively. As shown in  FIG. 2A , the exemplary integrated capacitive device  200  includes a material  210  embedded in a substrate  220 . According to one aspect of the invention, one or more pressure plates  250 - 2  and  250 - 2  are applied to the substrate  220  in order to compress the material  210  and thereby alter the capacitance of the integrated device  200 . The pressure plates  250  may be applied to opposite sides of the substrate  220  or a fixed plate (or the substrate itself) can be used on one side of the substrate  220 , while a single pressure plate  250  is applied to the opposite side of the substrate  220  to compress the material  210 , as would be apparent to a person of ordinary skill in the art. 
   The pressure plates  250  will selectively compress the embedded material  210  upon application of an appropriate control signal  260  to the pressure plates  250 . The pressure plates  250  may be embodied, for example, as bimetallic plates, piezo electric plates or plates controlled by a micro-electrical mechanical system (MEMS). The pressure plates  250  are in one position when a first voltage is applied and in a second position when a second voltage is applied. In the exemplary embodiment shown in  FIGS. 2A and 2B , the bimetallic pressure plates  250  will bow upon application of an appropriate control signal  260 . The control signal  260  determines the extent to which the embedded material  210  is compressed, and the resulting degree to which the capacitance is altered. 
   According to another aspect of the present invention, the capacitance of the integrated device  220  will vary depending on whether the integrated device  220  is in an uncompressed or compressed state, or an intermediate state in between. As shown in  FIGS. 2A and 2B , an input signal passes between input and output terminals  270 - i  and  270 - o , respectively, and the embedded material  210  provides a corresponding capacitance depending on whether the device  220  is in an uncompressed or compressed state. For example, the integrated device  220  may have a capacitance value of 20 Picofarads in an uncompressed state and a capacitance value of 100 microfarads in a compressed state. 
   In yet another variation of the present invention, the compression applied by the pressure plates  250  may be done continuously or intermittently. A continuous compression will introduce a different change in the electrical characteristics of the integrated electrical device than the vibration effect caused by an intermittent pressure. The pressure plates  250  may thus be controlled by transducers or similar devices that allow the pressure plates  250  to vibrate at a desired frequency. The shape of cavity in which the material  210  is retained may also be selected to achieve different results. 
   As previously indicated, a material  210  is placed inside the layers of the substrate  220 . As a signal passes through the material  210 , the capacitance of the integrated device is varied as the material is compressed. In one exemplary implementation of an integrated device  200 , the material  210  may be comprised of a dielectric material. The dielectric material can be in a grease or gel state. The capacitance value can be adjusted from Picofarads up to microfarads depending on the formulation. Generally, the material  210  is selected so that the response to the signal and the mechanical action is sufficient to produce the range of variation in the capacitance that is required. The capacitance material would be potentially anything from an air gap with parallel plates, ceramic materials, glass, tantalum oxide and different dopants added to Silicon. 
   In addition to the resistive and capacitive devices  100 ,  200 , discussed above in conjunction with  FIGS. 1 and 2 , respectively, an integrated inductance can be fabricated in accordance with the principles of the present invention, as would be apparent to a person of ordinary skill in the art. The embedded material is selected so that the response to the signal and the mechanical action is sufficient to produce the range of variation in the inductance value that is required. Currently, there are many iron filled materials used to produce magnetic fields and to vary the magnetic field base upon the shape of the material will then cause the inductance to also vary. 
   It is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.