1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a microelectromechanical (MEMS) sensor array technology that can be applied to many types of detection, including DNA, protein, antibody interactions, environmental contaminants, VCO's, toxins, and explosives.
2. Description of the Related Art
The present invention arises from a new area of recognition and development focused on the technology of low-temperature, crystalline-structure-processed devices, and in particular mechanical, mechanical and electrical, so-called MEMS (microelectromechanical), layered and stacked devices, and devices organized into monolithic arrays in layers, that opens up a broad new field of potential devices and applications not heretofore so inexpensively and conveniently made practical and practicable. This new field of possible devices, from which a number of inventions, one of which is specifically addressed in this disclosure, springs effectively from the recognition that internal crystalline-structure processing performed within the bodies of a wide variety of different materials, is capable of enabling fabrication of small (perhaps even down to devices formed from small molecular clusters), versatile, widely controllable and producible, accurate, mechanical, electromechanical and MEMS devices that can be formed very inexpensively, and, with respect to laser processing, in uncontrolled and room-temperature environments not requiring vacuum chambers, etc.
Especially, the invention offers significant opportunities for the building, relatively cheaply and very reliable, of very tiny semiconductor mechanical devices that can be deployed in dense two-dimensional and three-dimensional complex arrays and stacked arrangements. These devices can take on a large range of different configurations, such as individuated, single-device configurations, monolithic single-layer array arrangements of like devices, similar monolithic arrays of combined electrical and mechanical devices, and in vertically integrated and assembled stacks and layers of complex devices, simply not achievable through conventional prior art processes and techniques. By enabling room-temperature fabrication, otherwise easily damaged and destroyed layer-supporting substrates, including fabricated-device under-layers, can readily be employed.
The field of discovery and recognition which underpins the invention disclosed herein, can be practiced with a very wide range of semiconductor materials in arrays that can be deployed on rigid substrates of various characters, and on a wide range of flexible materials, such as traditional flex-circuit materials (polymers and plastics), metallic foil materials, and even fabric materials. Additionally, the field of development from which the present invention emerges can be employed with large-dimension bulk materials, as well as with various thin-film materials. The present invention is described in this broader-ranging setting. With regard to the latter category of materials, the process of this invention can take advantage of traditional thin-film semiconductor processing techniques to shape and organize unique devices, which are otherwise prepared in accordance with the internal crystalline-structure-processing proposed by the present invention, thus to achieve and offer mechanical properties in a broad arena of new opportunities.
In this setting, the invention disclosed in this document is specifically related to crystal-structure-processed semiconductor mechanical devices, either as individuated, single devices, or in arrays of devices organized into monolithic, layer-type arrangements, as well as to methodology and system organizations especially suited to the preparation and fabrication of such devices. The invention proposed a unique way, employing, for example, different types of lasers and other illumination sources, effectively to “reach into” the internal crystalline structures different semiconductor materials for the purpose of controllably modifying those structure to produce advantageous mechanical properties in devices, and at sizes very difficult and sometimes not even possible to create via prior art techniques.
From the drawings and the descriptions which now follow, it will become readily apparent how the present invention lends itself to the economic, versatile, multi-material fabrication and use of a large variety of devices, ranging from relatively large devices to extremely small device (as mentioned earlier), and including various forms of MEMS devices, without the fabrication of these devices, insofar as laser processing involved, necessitating the use of special controlled processing environments, or surrounding processing temperatures above typical room temperature.
With this in mind, the significant improvements and special contributions made to the art of device-fabrication according to the invention will become more fully apparent as the invention description which now follows is read in conjunction with the accompanying drawings.
MEMS devices are typically made on silicon wafers; using one of two well established techniques: bulk micro-machining or surface micro-machining. In both of these methods, the MEMS device is fabricated on a silicon wafer using standard IC -type fabrication equipment. Once the wafer is processed, the wafer is diced to form individual die. These MEMS die may or may not be integrated with electronic components (on CMOS). Once the die is cingulated, it must then be packaged in some form of package, similar to an IC package. This package is eventually inserted into a socket or bonded to a Printed Circuit Board (PCB) as part of an overall system, i.e., a cell phone. These packages can be quite elaborate, depending on the MEMS style and application, including vacuum package requirements. In addition, because many MEMS devices are required to move during operation, the package must provide a cavity that allows for this movement.
One problem with this type of MEMS packaging methodology is that the package is a very large proportion of the total MEMS device cost; on the order of 30- 70% of the overall cost. This packaging cost can, therefore, have a significant impact on the capability of such MEMS devices to penetrate cost-sensitive markets, such as the cell phone market.
Another problem with existing MEMS packaging is the noise inherent with the electrical connections between the MEMS package and the rest of the system. The bonding, wiring, and electrical interconnections associated with interfacing a MEMS device embedded in a package, to a circuit, necessarily adds impedance mismatches that result in noisy or low amplitude signals.
However, there is mounting evidence that MEMS technology can add value to systems, such as cell phones, in a market that is ripe for new technology, if only the packaging issue could be addressed. Continuing with the cell phone example, it is certain that the camera-on-cell phone has made a great impact on the market. The search is on for the next added functionality that can drive new expansion of the cell phone market.
MEMS are being considered for the following cell phone functions:                1) Motion capture (Accelerometer and gyroscope);        2) Microphones;        3) RF devices and RF modules;        4) Image capture;        5) Low power solutions;        6) Identification (biometrics);        7) Enhanced display functionality; and,        8) Personal health and safety monitoring.        
The issues preventing MEMS penetration into the cell phone market are cost and performance. As mentioned above, packaging is 30-70% of the MEMS device cost. This cost issue is preventing the integration of MEMS into cell phones, display systems, and many other types of electronic devices.
MEMS devices are a logical derivative of semiconductor IC processes that may be used to develop micrometer scale structural devices such as transducers or actuators, and they are typically fabricated on silicon substrates. MEMS devices typically interface physical variables and electronic signal circuits. The integration of MEMS into larger scale systems has been expensive to fabricate due to the process difficulties and the cost associated with integrating the MEMS standard IC technologies, such as CMOS. The processes used to fabricate MEMS on glass offer the advantage that the integration of electrical and mechanical functions is easily done. In this way, system level integration is possible and cost effective.
TFTs are formed through deposition processes that create thin films of silicon (Si) and insulator material. While the resulting TFTs may not have the switching speed and drive capability of transistors formed on single-crystal substrates, the transistors can be fabricated cheaply with a relatively few number of process steps. Further, thin-film deposition processes permit TFT devices to be formed on alternate substrate materials, such as transparent glass substrates, for use in liquid crystal displays (LCDs). More specifically, the TFTs include a deposited amorphous Si (a-Si) layer. To improve the performance of the TFT, the a-Si may be crystallized to form poly-silicon, at the cost of some extra processing. The crystallization procedures are also limited by the temperature sensitivity of the substrate material. For example, glass substrates are known to degrade at temperatures over 650 degrees C. Large scaled devices, integrated circuits, and panel displays are conventionally made using thin-film deposition processes.
MEMS devices are a logical derivative of semiconductor IC processes that may be used to develop micrometer scale structural devices such as transducers or actuators. MEMS devices interface physical variables and electronic signal circuits. MEMS structures are varied and, therefore, more difficult to standardize, as compared to the above-mentioned thin film processes. On the other hand, it may be possible to develop MEMS devices by engineering modifications to well-developed silicon IC processes. Many of the MEMS devices that have been fabricated to date have more theoretical than practical application, as the devices are often difficult and expensive to make. For the same reason, larger scale systems using MEMS components, have been expensive to fabricate due to the process difficulties and the cost associated with integrating the MEMS and IC technologies. For example, transistors and associated MEMS structures have been fabricated on bulk Si substrates, However, the etching processes needed to form a bulk silicon MEMS -are more difficult to control, dramatically limit available process steps, and require long etch times. These limitations make these devices unsuitable for low-cost integrated systems. Alternately, MEMS structures made using high temperature LPCVD thin films have been built with conventional sensing schemes such as capacitive and/or piezoresistive bridges, generating reasonable output signals. However, these sensing schemes cannot be applied to low temperature TFT process, because the changes in electrical characteristics induced as a result of stress change are too small to be practically measured.
Sensor array technology has been very successfully applied to gene expression studies (among other applications). Current microarray technology is based primarily on optical detection methods. Two main types of DNA microarrays are THE synthesized ogleotide type, such as those manufactured by Affymetrix, and “spotted core” arrays that are made by applying materials of interest to glass slides using automated arrayers or ink jet technology. Several problems plaque current microarray technology:
1) High cost: current microarray technology is very expensive with the most expensive being the Affymetrix-type. The “genechip” is a single use device that costs on the order of $300 to $500 per chip. In addition, several pieces of additional process equipment are required: among them a washing station and scanner. The process requires the scanning of the “genechip” (with the material of interest applied to the chip) with a laser, florescent material on the chip is activated and a light imager records the image of the florescent pattern. Then, the result must be interpreted using templates to analyze the image.
2) Low throughput: While current microarray technology has produced a very high volume of data for genetic research, the process is still relatively slow. For example, a DNA hybridization experimental process takes a minimum of several hours and more likely overnight to complete.
3) Inaccuracies: The current DNA microarray technology produces results with inaccuracies such as false positives.
4) Bulky system: The current microarray technology requires an assortment of process equipment. In addition to the equipment required to prepare the array, a laser scanner and image detection system are required to read the result. Thus, this technology cannot produce a portable solution for microarray applications.
It would be advantageous if active devices could be formed in a MEMS mechanical structure using the same, shared process steps.
It would be advantageous if MEMS devices could be packaged as part of the overall process of fabricating electronic (active) devices on a circuit board or display.
It would be advantageous if a TFT could be integrated with a MEMS mechanical structure using the same, shared thin-film deposition and annealing processes.
It would be advantageous if a stress change sensing scheme could be formed in a MEMS mechanical structure using the same, shared process steps as TFT fabrication.