Volumetric electro-optical recording

Details Volumetric electro-optical recording Volumetric electro-optical recording

2001-03-19

2004-02-03

Lam, David (Department: 2818)

Static information storage and retrieval

Radiant energy

Electroluminescent and photoconductive

C365S111000, C365S175000

Reexamination Certificate

active

06687149

ABSTRACT:

FIELD OF THE INVENTION
This present invention deals with the semiconductor type of memory devices capable of writing and reading information optically and having a multi-layer structure with multiple information layers as well as writing and reading arrangements for writing to and reading from such devices.
BACKGROUND OF THE INVENTION
Rapid progress has been made in data communication via the Internet by using mobile digital devices that combine the functionality of a PC. Such progress necessitates the development of non-volatile miniaturized semiconductor memory devices, known as solid state memory. However, the current capacity of the solid state memory devices does not meet the demand of the multi-gigabyte capacity needed for various computing applications. It also should be noted that these devices are expensive to make. One type of such devices, namely, DRAM, is progressing remarkably and is entering an era of gigabit storage capacity. DRAM increases its integration density by migrating from the initial structure that includes a plurality of transistors in one cell to a structure that consists of one transistor per cell. In the gigabit memory era, however, a capacitance of the storage capacitor is not sufficient for additional capability increases even by adapting trenched and stacked structures. Various technology adaptations utilize high dielectric constant materials as insulating layers in capacitors, and yet many problems are unresolved even till now. The conventional DRAMs with the trenched or stacked structures, as well as DRAMs that employ high dielectric constant materials for storage capacitors, require complicated fabrication processes and expensive manufacturing equipment. A cost of some ten billion dollars is estimated to be necessary to realize a manufacturing line which can mass manufacture semiconductor memory devices with an improved integration density. Moreover, since the conventional DRAMs are designed essentially on the basis of a planar (two-dimensional) layout, they can not be further miniaturized by the means of lithography. Thus, a technical barrier appears in the conventional solid sate semiconductor memory technologies, and a breakthrough in the technical barrier is necessitated.
A possible solution of these problems relates to an approach that combines optical signal processing technology and microelectronics. Originally this approach has been proposed for the utilization in the optical computers. A main advantage of the optical processing is that an individual element of the system can communicate simultaneously with an enormous number of other elements. This advantage originates from the fundamental nature of optical beams that do not interact with each other even in the case of crossing of their light path. One of the early inventions has been disclosed in U.S. Pat. No. 3,623,026 (1971), where a semiconductor device utilized for optical storing and reading of information has been proposed. This method utilizes a conductor-insulator-semiconductor structure (CIS) that serves as a capacitor for data storage. A thin layer of insulating material separates the conductor from the semiconductor. When the CIS structure is charged to the predetermined voltage and exposed to the radiation of band gap energies passing through the substantially transparent conductor and insulator layers, minority carriers are generated in the semiconductor bulk near or in the depletion region and move to the insulator-semiconductor interface. Reversing the voltage changes the direction of the electric field, thereby injecting minority carriers into the semiconductor and causing an emission of electromagnetic radiation. New approaches for an efficient and low cost technology are disclosed in U.S. Pat. No. 5,504,323, in which the device combines functions of the light emitting diode and photo-receiver. In this case, a positively biased diode functions as a light emitter. When a negative bias is applied, it becomes a highly efficient photo-diode. The described devices are an example of volatile memory, which needs continuous power supplying. A non-volatile optical semiconductor memory device was proposed recently U.S. Pat. No. 6,147,901 (2000). In this case, a memory cell utilizes vertically stacked structures comprised of p-i-n-i-p or n-i-p-i-n structures, where p means p-type semiconductor, n is n-type semiconductor and i is the intrinsic type of semiconductor. The electron-hole pairs are generated under the light illumination in the p
-junction zone and under the biased voltage, electrons tunnel in the i-type semiconductor and are trapped there by the impurities. Such a structure is known as an electrical write-erase non-volatile memory.
The references mentioned above disclose types of memory cells and do not suggest any write/read device. PCT International Application No. WO 97/48009 A1 (1997) suggests an optical logic element that comprises a light source, a memory sub-layer, and a photo-sensor sub-layer. A plurality of these elements are assembled in memory or logic layers that could be integrated into a 3D multi-layer device. As a material for the memory device, the reference suggests a wide variety of materials which change their optical properties when exposed to the illuminating light source. These materials could be liquid crystals, photo-chromes or photo-chemicals. However, a possible realization of this idea is rather problematic due to the limited sensitivity of the photosensitive sub-layer. For example, the most advanced modem CCD matrix has a total charge capacity per pixel of about 10
5
electrons in a size of 10 &mgr;. In the pixel of the proposed device having the size of 0.5 &mgr;, this value will be reduced to 250 electrons, which means that the working average value of the charge is about 100 electrons. During the reading, this amount of electrons corresponds to the shot noise of 10%, which is unacceptable for most of the applications.
The above described technical barriers exist today in the miniature high capacity semiconductor memory devices that are capable of storing and reading information with a high data rate due to the processes of the absorption and emission of light
SUMMARY OF THE INVENTION
The present invention resolves the above described limitations and has a way to provide a new type of solid state semiconductor memory devices which can retain stored content for a certain time period even after removal of the power supply. This is achieved by employing methods of light absorption and emission.
Another object of the present invention is to provide a semiconductor memory device capable of writing data optically and erasing data electrically and/or optically with a high rate of speed at the same time preserving the stored content even after removal of the power supply.
A further object of the present invention is to provide a semiconductor memory device capable of reading data optically at a high rate of speed.
A further object of the present invention is to provide a semiconductor memory device capable of being manufactured with the relatively easy fabrication processes and at lower costs.
A further object of the present invention is to provide a semiconductor memory device having a simple structure capable of being miniaturized with a relative ease.
A further object of the present invention is to provide a combination of the different types of semiconductor memory devices such as DRAM, SDRAM, and PROM combined with the functions of a typical CPU such as arithmetic and logic units. All of the functions in such types of devices could be combined in a single chip.
To achieve the required objectives, a first feature of the present invention lies in the arrangement of a sub-layer comprised of a two-dimensional array of electroluminescent cells organized into rows and columns, which are individually electrically addressable through the system of transparent electrodes disposed in rows and columns. The electroluminescent cells are located between the crossings of the electrodes. The electroluminescent materials could be organic or non-organic s

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