Nano-vacuum-tubes and their application in storage devices earned U.S. Patent 7,667,996 for Contour Semiconductor, Inc. (North Billerica, MA)
According to inventor Daniel R. Shepard, the scale of the devices in a diode array storage device, and their cost, are reduced by changing the semiconductor based diodes in the storage array to cold cathode, field emitter based devices. The field emitters and a field emitter array may be fabricated utilizing a topography-based lithographic technique.
Devices constructed with nano-vacuum-tubes will find applicability in such areas as storing digital text, digital books, digital music, digital audio, digital photography (wherein one or more digital still images can be stored including sequences of digital images), digital video, and digital cartography (wherein one or more digital maps can be stored), as well as any combinations thereof. These devices can be embedded or removable or removable and interchangeable among devices.
They can be packaged in any variety of industry standard form factors including Compact Flash, Secure Digital, MultiMedia Cards, PCMCIA Cards, Memory Stick, any of a large variety of integrated circuit packages including Ball Grid Arrays, Dual In-Line Packages (DIP's), SOIC's, PLCC, TQFP's and the like, as well as in custom designed packages. These packages can contain just the memory chip, multiple memory chips, one or more memory chips along with a controller or other logic devices or other storage devices such as PLD's, PLA's, micro-controllers, microprocessors, controller chips or chip-sets or other custom or standard circuitry.
One of the simplest forms of data storage devices is the diode array storage device. However, a problem with diode array storage devices is that as the size of the array increases, the number of non-addressed diodes connected between a given selected row or column of the array and the non-addressed columns or rows of the array, respectively, also becomes very large.
While the leakage current through any one non-addressed diode on the selected row or column will have little impact on the operation of the device, the cumulative leakage through multiple thousands of non-addressed diodes can become significant. This aggregate leakage current can become great enough that the output voltage or current or charge can be shifted such that the threshold for distinguishing between a one state and a zero state of the addressed diode location can become obscured and can result in a misreading of the addressed diode location.
Furthermore, as the arrays are scaled to smaller and smaller geometries, the semiconductor structure can become a limiting factor in that the layers of semiconducting material must be kept thick enough to control reverse leakage currents; however, to further reduce the scale of the devices the thickness may also have to be reduced to facilitate such scaling
Shepard’s invention facilitates the reduction of scale of the devices in a diode array storage device and reduces the cost. In general, this is accomplished by utilizing field emitter-based devices, e.g., diodes or triodes, rather than semiconductor-based diodes. Processes in accordance with the invention will have fewer fabrication steps than a semiconductor material-based process, resulting in an economic advantage.
The field emitter contemplated is similar to the classic vacuum tube device called the diode, which is a two ("di")-electrode ("ode") non-linear device that conducts current more easily in one direction than the other. The present invention provides an enhancement to all types of arrays of diodes or arrays of other nonlinear conducting elements including: storage devices, programmable logic devices, display arrays, sensor arrays, and many others. Contour’s patent also includes methods for manufacturing field emitters for these or other purposes in a semiconductor process line.