Patent Publication Number: US-8966730-B1

Title: Method of manufacturing a sensor network incorporating stretchable silicon

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 12/389,196, filed Feb. 19, 2009, now U.S. Pat. No. 7,498,147, entitled “SENSOR NETWORK INCORPORATING STRETCHABLE SILICON”, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The field of the disclosure relates generally to sensor networks, and more specifically, to methods and systems relating to sensor networks that incorporate stretchable silicon. 
     Existing solutions for monitoring, for example, the structural health of large areas, include interconnecting networks of sensors based on electrically conductive wires and optically conductive fibers. While fiber optic communications enables low power devices in certain communications systems, it does not enable addressing of an array of sensors without the complexity of interconnections among network nodes. Other considerations include manufacturability, mechanical connection of input/output signals, scalability, cost and reliability of wiring/fiber-optic harnesses, power busses, and data busses. 
     BRIEF DESCRIPTION 
     In one embodiment, a sensor network is provided that includes a stretchable silicon substrate and a plurality of nodes fabricated on the stretchable silicon substrate. The nodes include at least one each of an energy harvesting and storage element, a communication device, a sensing device, and a processor. The nodes are interconnected via interconnecting conductors. 
     In another embodiment, a method for fabricating a network is provided. The method includes stretching a silicon medium over a desired area, processing the stretched silicon medium to generate a number of nodes thereon, and utilizing conductive paths within the stretchable medium to redundantly interconnect the generated nodes to form the network. 
     In still another embodiment, a network for monitoring a structure is provided. The network includes a stretchable silicon substrate, a plurality of sensors fabricated on the stretchable silicon substrate, at least one communication device fabricated on the stretchable silicon substrate, and at least one energy harvesting and storage element fabricated on the stretchable silicon substrate. The stretchable silicon substrate includes a plurality of conductive paths therein that interconnect the plurality of sensors, the at least one communication device, and the at least one energy harvesting and storage element. The network is configured for attachment across a structure, dispersing the sensors. Data from the sensors is communicated to an external device via the at least one communication device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system block diagram illustrating a sensor network fabricated using stretchable silicon in an advantageous embodiment. 
         FIG. 2  is a diagram illustrating a sensor network in another advantageous embodiment, that includes stretchable silicon interconnecting energy harvesting and storage elements, wireless and wired communication devices, micro-sensors, and network management processors. 
         FIG. 3  is a flowchart illustrating a method for fabricating a sensor network using stretchable silicon in another advantageous embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram of a sensor network  10  that is based on stretchable silicon. In the illustrated embodiment, three nodes have been fabricated on a stretchable silicon substrate. The three nodes include a power supply node  12 , a processor node  14 , and a sensor node  16 . The nodes are interconnected via interconnecting conductors  20 ,  22 , and  24  formed in the stretchable silicon substrate. 
     In one embodiment, the power supply node  12  may be an energy harvesting and storage element. For example, power supply node may be a piezo-electric generator that is integrated with silicon-based Nano/Micro-Electromechanical Systems (N/MEMS) In this embodiment, the combination is able to generate and store electrical power. The power supply node  12  may provide such power to both the processor node  14  and the sensor node  16 . In other embodiments, a plurality of power supply nodes  12  may be distributed across the stretchable silicon substrate providing power to nodes hosting such processing, sensing, or communication functions. 
     The processor node  14  includes a processing function and may include an RF receiver and transmitter  30  for communicating with portions of the sensor node  16  that are capable of communicating wireless methods. The processor node  14  may further include processing capabilities for communicating via a digital vehicle network interface  40 , for example. The embodiment of  FIG. 1  may include an RF-to digital inverter  32  and a digital-to-RF converter  34  facilitating communications between the vehicle network  40  and the sensor node  16  via the RF receiver/transmitter  30 . The processor node  14  may be configured to manage and monitor the behavior of sensor network  10 , including power generation and consumption, data acquisition, and communications both within the sensor network  10  and with external devices such as vehicle network  40 . 
     The sensor node  16 , may have a wireless operating capability, though alternative embodiments are operable through wired operating capabilities. In both configurations, the sensor node  16  includes a sensor element  50  and a communication element  52 . The sensor element  50  may include integrally formed signal conditioning circuitry or signal conditioning circuitry may be physically separated from the sensor element. 
     The sensor node  16  as shown in  FIG. 1  is configured for wireless operation, similar to the processor node  14  described above. However, embodiments are contemplated where the stretchable silicon medium is utilized as a communications interconnect between the sensor node  16  and the processor node  14 , as shown by the stretchable silicon interconnect  20 . Stretchable silicon interconnect  22  is utilized in the illustrated embodiment to provide the power to the processor node  14  from the power supply node  12 , while the stretchable silicon interconnect  24  is utilized in the illustrated embodiment to provide the power to the sensor node  14  from the power supply node  12 . 
       FIG. 2  is an illustration of a sensor network  100  fabricated using stretchable silicon  105 . In the illustrated embodiment, the network  100  includes a plurality of components that have been fabricated on the stretchable silicon  105 . The components include, for example, energy harvesting and storage elements  110 , communication devices  120 , sensors  130 , and network management processors  140 . The communications devices  120  may include both wireless and wired devices. As described herein, the plurality of components are integrated on a medium of stretchable silicon  105 , which provides multiple conductive paths  160  (interconnects) formed therein which provide, for example, conduction of electrical power from the energy harvesting and storage elements  110  to the communication devices  120 , sensors  130 , and network management processors  140 . 
     The conductive paths  160  also provide for at least some of the communications between the above listed components. As described further herein, and in one embodiment, the stretchable silicon  105  forms a portion of an autonomous network of wireless sensors. A high reliability results due to the redundancy built into the network  100  with stretchable silicon interconnects  160 . As such, the network  100  may utilize use alternative paths between the various network components to achieve reliable communications between the sensors  130  and the existing vehicle communication network. As the illustrated network  100  has its own power source, energy harvesting and storage elements  110 , the addition of such a network does not tax vehicle power systems. 
     The stretchable silicon medium  105  is an excellent enabler because every node formed thereon can be converted into a component that provides a desired function. Examples include a processor function and miniature sensor nodes. In one embodiment, the nodes have a size of about 200 micrometers. In one embodiment, the stretchable silicon medium  105  is processed from a foundry-processed, monolithic silicon die, of a size between one centimeter and twenty centimeters and stretched over a larger area. The process results in a plurality of robust conductors that run between the various nodes that are fabricated on the medium  105 . 
     Network  100  resolves at least some of the prior problems that have been associated with weight and supportability of energy storage devices, complexity of interconnections among network nodes, manufacturability, mechanical connection of input/output signals, and scalability. More specifically, a system incorporating network  100  enables networked sensor coverage of large areas with multiple applications. One such application involves monitoring structural health of a structure where a plurality of the above mentioned sensors provide data to a processing element which can be queried by an external system. Other applications include the monitoring of air flow over aerodynamic surfaces utilizing applicable sensors fabricated on medium  105  and the monitoring of ice accretion and other hazardous conditions that may be encountered with the use of an aerospace structure. 
     Turning now to the individual components of network  100 , energy harvesting and storage elements  110  provide power to the other elements of network  100 . In one embodiment, a nano-piezoelectric generator effect is utilized within element  110  to convert mechanical stress into electrical current or voltage for powering the other components of network  100 , including any sensors that may be fabricated on the medium  105 . In one specific embodiment, zinc oxide (ZnO) nanowires are utilized in network  100 . These ZnO nanowires are grown using chemical synthesis on a substrate with any curvature and materials nature. These ZnO nanowire generators produce power on the order of milliwatts in an area that is about one square millimeter. 
     A power output associated with such energy harvesting and storage elements  110  proportionally increases as the nanowire substrate area is expanded. Also, these devices are easily integrated with stretchable silicon based nano/micro electronics devices to develop robust Nano/Micro-Electro-Mechanical Systems (N/MEMS). In certain embodiments, the energy harvesting nodes of elements  110  incorporate capacitance-based or other energy storage components to meet the energy demands of the network  100 . 
     In regard to the communication devices  120 , at least one embodiment incorporates wireless transceiver nodes allowing data to be transmitted to and from the network  100 . Such embodiments are referred to as single chip transceivers based on silicon systems. One embodiment incorporates the stretchable silicon in the fabrication of transceiver integrated circuits including the development of RF and baseband components of wireless transceivers on a single die. Wireless transceiver nodes can be directly connected to external devices. 
     Silicon offers a high level of integration and a low cost which is desirable for large scale manufacture, and also has the potential of reducing the power consumption. Lower power consumption allows for cheaper packaging materials such as plastic which greatly reduces the cost of a chip. For integrated solutions using silicon, bipolar and CMOS are the most popular process technologies. Bipolar technologies offer high speed and are most commonly used in analog applications. CMOS has a lower limit frequency but offers a high level of integration which is attractive for digital applications. 
     The sensor nodes  130  form a network constructed with silicon based devices. In various embodiments, the sensor nodes  130  may include sensors for structural health monitoring, temperature sensors, pressure sensors, vibration sensors, ice accretion sensors, dynamic air flow separation sensors, and other sensor types. In one embodiment, the sensor nodes  130  include signal conditioning circuitry, providing an interface between the sensor nodes  130  and the communications devices  120  and/or an interface between the sensor nodes and network management processors  140 . Network management processors  140  may monitor the network for active sensor nodes  130  and determine if they belong to the network. The power required by the communications device  120 , sensor nodes  130  and the network management processors  140  is supplied, in various embodiments, by the energy harvesting and storage elements  110  described above. 
       FIG. 3  is a flowchart  200  further illustrating a method for fabricating a sensor network such as those described herein incorporating stretchable silicon. The method illustrated in the flowchart  200  includes stretching  202  a silicon medium over a desired area, processing  204  the stretched silicon medium to generate a number of nodes thereon, and utilizing  206  conductors within the stretchable medium to redundantly interconnect the generated nodes to form the network. 
     As further described herein, processing  204  the stretched silicon medium may include generating one or more of an energy harvesting and storage element, a communication device, a sensing device, and a processor, while utilizing  206  conductors within the stretchable medium may include routing power from energy harvesting and storage elements to the various communication devices, sensing devices, and processors. 
     Processing  204  the stretched silicon medium, in one embodiment, includes generating at least one communications device with a wireless communications capability. In another embodiment, processing  204  the stretched silicon medium includes generating at least one processor capable of communicating with an external network. As further described herein, the method described by flowchart  200  is useful for multiple applications, and therefore, processing  204  the stretched silicon medium may include, but is not limited to, generating sensors for structural health monitoring and management, generating ice accretion sensors, and generating sensors configured for sensing dynamic flow separation of the air surrounding the sensor. 
     Various embodiments described herein may be used for structural health monitoring and management, for example, of aircraft and other vehicles. In such applications, the stretchable silicon substrate is capable of being stretched out, for example, up to 100 times its original size. In the structural health application, such a substrate may be attached across a relevant portion of the structure. In the configuration, sensors are able to sense changes in the environment, provide data to network processors such as network management processors  140  which in turn utilize communications devices  120  to communicate the sensor data to an external system. Examples of applications outside of structural health monitoring include dynamic flow separation of the surrounding air, and the monitoring of ice accretion on structures. 
     The autonomous network of wireless sensors described herein accommodates the rigorous configuration control demands of aerospace applications and enhances sensor designs and construction methods suitable for installation in hostile environments. A wide range of temperature sensors, pressure sensors and flow sensors for harsh and demanding environments can be utilized in aircraft and aero engines where unique applications are desired. Also, the described network has the capability of incorporating advanced data systems architectures that are necessary to communicate, store and process massive amounts of health management data from large numbers of diverse sensors. 
     In one example, network  100  can be configured to perform as a portion of an Integrated Vehicle Health Management (IVHM) system that will provide real-time knowledge of structural, propulsion, thermal protection and other critical systems for optimal vehicle management and mission control. In such systems, on-board, real-time sensing systems are a critical component of a vehicle health management system. To provide such capability, network  100  includes sensors that have an ability to withstand harsh aerospace operating environments, while also having minimal size, weight, and power requirements. 
     This written description uses examples to disclose various embodiments, including the best mode, and also to enable any person skilled in the art to practice those embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.