Image analysis – Applications – Personnel identification
Reexamination Certificate
1998-10-07
2001-10-16
Boudreau, Leo (Department: 2621)
Image analysis
Applications
Personnel identification
C382S312000, C382S108000
Reexamination Certificate
active
06304666
ABSTRACT:
BACKGROUND OF THE INVENTION
There is a variety of applications in which it is useful to be able to provide a two-dimensional map of the distribution of charge or of potential across a surface. This map is normally in electronic form for use by a computer for processing of the information in the map or for storage in a memory medium of some sort.
Many of these applications involve the storing or processing of images such as writings, drawings, and photographs. etc. Typically, an optical image of the writing, drawing, picture, signature, etc. is transformed by a lens to fall onto an array of photodetectors which then provides an electronic description of the intensity of the light falling onto the individual elements of the photodetector array.
Other applications involve the creation of such images or other patterns via stylus input onto an electronic tablet or screen or via the sensing of fingerprints by means of a pressure-sensitive surface or directly by charge variations on the skin surface that correspond to the fingerprint. These images or patterns are not sensed optically but are, instead, sensed by charge or field inputs that are applied to selected areas of a sensing array. Such images and patterns may also be created by the measurement of thermal variations.
These applications are presently being met in the art by a variety of different devices, but most of them require significant amounts of power and are unable to store a sensed state without the further application of power to refresh their associated electronic memory storage units.
The methods currently used to perform these tasks may be costly in both time and material. For example, the recognition of an image usually requires some scanning system where the image is swept or scanned optically. The signal corresponding to pixels of the image detected by a photosensitive detector is then transformed into a digitized image. Certain applications that involve heavy use by the public, such as reading the finger print of a client at a point of sale for comparison to an electronic image of a finger print stored on a checking card (“smart card”) will require devices that are rugged and inexpensive. Similar demands are set on all applications where one is required to install large numbers of such sensing and identification devices in circumstances such as those found involving charging the cost of a telephone call from a public phone via a smart card, identifying passengers in transit in air terminals, transactions at ATM machines, identification at security checkpoints and the like.
It would therefor be exceedingly useful if a sensing device existed that could perform these various applications and that had at least some of the following characteristics: simple and robust in construction, low power, low cost, readily portable as necessary and non-volatile. No such device is known at this time however.
BRIEF SUMMARY OF THE INVENTION
The above-referenced patent application, “Memory Device Using Movement of Protons,” describes a new type of memory device in which the memory action is integrated into the gate oxide of the field effect transistor. In this device, charged particles (protons) are introduced into the gate oxide of the transistor by a sequence of thermal treatments. These charges can be swept up or down across the thickness of the oxide by the application of an appropriate potential to the gate electrode with respect to the substrate. This device is nonvolatile because, when the potential is removed, the mobile charges remain in their last position, thus maintaining the channel of the FET in either a conductive or non-conductive state after the potential has been removed. This nonvolatile On or Off state allows the FET to be used as a binary memory element.
The present invention recognizes that this nonvolatile FET (NVFET) can be used as a charge sensitive detector if the charge is placed on the gate of the NVFET. Rather than use the NVFET simply as a memory device, one can, with suitable modifications, use it to detect charge and to store its state electrically. Such a detector can be expressed as an array of NVFETs formed on a planar surface with each transistor addressed electrically to read it ON/OFF state. In other words, the charge established on the gate electrode of the NVFET will displace the mobile charges to a position such that they switch the transistor into the OFF or the ON state which is read as a source-drain current of the transistor which is either essentially zero (or very small) or substantially larger. The ON/OFF state of each individual transistor remains essentially “stored” in the device until a general potential is applied to the gates of all the NVFETs in the array, resetting all of the transistors into their basic mode. The particular implementation for applying a charge to the gates of the NVFET array can vary depending upon what needs to be sensed. The following paragraphs give summaries of several such embodiments of the invention.
One preferred embodiment of this invention is as a fingerprint detector. In the case of the operation of a normal MOSFET, one varies the potential applied to the gate electrode with respect to the source electrode by means of a voltage source and a conducting wire connected to the source and gate contacts. For applications such as the recognition of fingerprints, one can sense a ridge or a valley of a fingerprint by either placing a charge on the skin surface or by utilizing a piezoelectric polymer that will create a charge where the ridges in the fingerprints press down on the polymer. A thermoelectric or pyroelectric film may also be used. In any case, only the ridge will be sensed directly since only the ridge will contact a surface of the detector above the NVFET array. The charge from the ridges of the fingerprints will displace the mobile charges in the oxide layer of the NVFETs directly below the ridges and so switch the states of the individual, closely spaced transistors in the array. Once the states of those transistors touching the ridges of the fingerprints have been switched, the image of the fingerprint has been captured in a nonvolatile form and can then be read out electronically for further use or processing.
In another preferred embodiment, the invention may be employed to store handwriting. This application is similar to the fingerprint storage described above, but, instead of sensing the ridges of fingerprints, the point of a stylus is sensed. The point can be connected to a source of potential such that it is polarized either negatively or positively with respect to the source electrode of each NVFET in the array. Alternatively, the point is not charged but pushes down onto a piezoelectric layer that creates a potential between the contacted gate electrodes and the surface/sources of the affected transistors in the array. Only those transistors over whose gates the point will have passed will have had their electrical state modified so that when subsequently the electrical state of each transistor in the array is addressed, an electrical image of the written impression will be read. Such a recorded image may be transferred to a computer memory where it can be stored as information or used for purposes of comparison with an image already stored, i.e., a signature. The information written in the NVFET array can then be erased, and the array of transistors can be reset into its basic configuration by application of an erase potential simultaneously to the gates of all the transistors in the array. A subsequent writing and storage can then be commenced.
In yet another preferred embodiment, the invention may be employed as a scanner to digitize optical images. Scanners utilize arrays of photodetectors to convert the optical image into a digitized image. The photodiodes detect the light transmitted or reflected from a surface/object and convert the optical image into an electrical form which can be gray scale or binary. In the present embodiment, an array of charge sensitive NVFETs, that is capped by a photoconductive layer and a transparen
Devine Roderick A. B.
Warren William L.
Boudreau Leo
Durkis James C.
Kehl Dickson G.
Lucas John T.
The United States of America as represented by the United States
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