Write-once-read-many-times Research Articles

A low switching voltage organic-on-inorganic heterojunction memory element utilizing a conductive polymer fuse on a doped silicon substrate

We present a simple, nonvolatile, write-once-read-many-times (WORM) memory device utilizing an organic-on-inorganic heterojunction (OI–HJ) diode with a conductive polymer fuse consisting of polyethylene dioxythiophene:polysterene sulfonic acid (PEDOT:PSS) forming one side of the rectifying junction. Current transients are used to change the fuse from a conducting to a nonconducting state to record a logical “1” or “0”, while the nonlinearity of the OI–HJ allows for passive matrix memory addressing. The device switches at 2 and 4 V for 50 nm thick PEDOT:PSS films on p-type Si and n-type Si, respectively. This is significantly lower than the switching voltage used in PEDOT:PSS/p-i-n Si memory elements [J. Appl Phys. 94, 7811 (2003)]. The switching results in a permanent reduction of forward-bias current by approximately five orders of magnitude. These results suggest that the OI–HJ structure has potential for use in low-cost passive matrix WORM memories for archival storage applications.

Electrochromic conductive polymer fuses for hybrid organic/inorganic semiconductor memories

We demonstrate a nonvolatile, write-once-read-many-times (WORM) memory device employing a hybrid organic/inorganic semiconductor architecture consisting of thin film p-i-n silicon diode on a stainless steel substrate integrated in series with a conductive polymer fuse. The nonlinearity of the silicon diodes enables a passive matrix memory architecture, while the conductive polyethylenedioxythiophene:polystyrene sulfonic acid polymer serves as a reliable switch with fuse-like behavior for data storage. The polymer can be switched at ∼2 μs, resulting in a permanent decrease of conductivity of the memory pixel by up to a factor of 103. The switching mechanism is primarily due to a current and thermally dependent redox reaction in the polymer, limited by the double injection of both holes and electrons. The switched device performance does not degrade after many thousand read cycles in ambient at room temperature. Our results suggest that low cost, organic/inorganic WORM memories are feasible for light weight, high density, robust, and fast archival storage applications.

A polymer/semiconductor write-once read-many-times memory.

Organic devices promise to revolutionize the extent of, and access to, electronics by providing extremely inexpensive, lightweight and capable ubiquitous components that are printed onto plastic, glass or metal foils. One key component of an electronic circuit that has thus far received surprisingly little attention is an organic electronic memory. Here we report an architecture for a write-once read-many-times (WORM) memory, based on the hybrid integration of an electrochromic polymer with a thin-film silicon diode deposited onto a flexible metal foil substrate. WORM memories are desirable for ultralow-cost permanent storage of digital images, eliminating the need for slow, bulky and expensive mechanical drives used in conventional magnetic and optical memories. Our results indicate that the hybrid organic/inorganic memory device is a reliable means for achieving rapid, large-scale archival data storage. The WORM memory pixel exploits a mechanism of current-controlled, thermally activated un-doping of a two-component electrochromic conducting polymer.

Effect of heat treatment on the optical properties of amorphous Sb 2S 3 film: The possibility of optical storage

The optical absorbance, refractive index and absorption edge of vapour deposited amorphous Sb 2S 3 films are studied systematically as a function of annealing temperature in the range 160°C > T > 23°C. As deposited films continuously loose sulphur above 60°C as determined by ESCA and this loss affects their measured optical properties. Modification of optical properties upon heating to T = 160°C opens the possibility of a WORM (write once read many times) kind of optical storage as demonstrated in laser irradiation experiment.

Data warehouse processing and query by mail

Much effort in I/S is currently going into creating "Data Warehouses." These are stores of data periodically extracted from older legacy applications, converted to common standards and made accessible for user analysis. The warehouse acts as a WORM (Write Once, Read Many times) storage. Where the extract and transfer is performed nightly, they provide access to what is termed "Near Operational" data and can be used to replace much of the existing reporting. In other cases they are used to store mostly historical data for analysis of trends, market impact, financial status and do on. While often implemented with a variety of different clean up tools, languages, data base products and query tools, this article describes an implementation done almost entirely with APL. It includes a query capability termed "Query by Mail" which enables anyone with access to E-Mail to send queries to the Warehouse and receive responses or extracts of data by return mail. The "query" includes customized analysis of field content to allow identification of fields and records containing invalid data. Built upon a proprietary inverted file system, it provides rapid response to user queries and little load on the server system.

Animated visualization of a high resolution color three dimensional digital computer model of the whole human head

The interactive visualization of animated images through a computerized three dimensional (3D) full color model of an unstained cadaveric human head is presented. Serial full color images were taken of the blockface of a cryomicrotomed frozen human head every 200 μm. From this series of images a three dimensional digital model with a resultant pixel resolution of 200 μm 3 was created on a UNIX workstation. Using this database, resampled images were computed along orthogonal axes and written sequentially to a write-once-read-many times (WORM) videodisc unit. Playback of this customized videodisc dataset provides animations of the digitally reconstructed slices and 3D reconstructed surface models. An interactive interface to the animated sequences is provided through a PC based tutorial package. This tutorial program is able to access videodisc frames to display animations and labeled still images in a software window to illustrate various neuroanatomic topics. The technique of animation as applied to this high resolution 3D model provides insight into complex spatial relationships and has great potential in research and as a teaching tool in the neurosciences.

Optical Storage Disk Technology

Optical storage of digital information has reached the consumer market in the form of the compact audio disk. In this technology, information is stored in the form of shallow pits embossed in a polymer surface. The surface is coated with a reflective thin metallic film, and the digital information, represented by the position and length of the pits, is read out optically with a focused, low-power (5 mW) laser beam. When used for information storage for a computer this device is called a CD-ROM, a Compact Digital-Read Only Memory. The user can only extract information (digital data) from the disk without changing or adding any data. That is, it is possible to “read” but not to “write” or “erase” information.While it is an advantage to have permanently stored information in some cases — for example when listening to Beethoven's Ninth Symphony—in other situations the read-only feature is not appropriate. For most computer applications, it is essential that the user be able to store information on the disk and read it back at will. For example, in a word processing task—such as typing this article — it is often necessary to store the document on a disk. Optical data storage for this purpose is available in the form of a Write Once Read Many times (WORM) optical disk drive. The operating principle in a WORM drive is to use a focused laser beam (20 – 40 mW) to make a permanent mark on a thin film on a disk. The information is then read out as a change in the optical properties of the disk, e.g., reflectivity or absorbance. These changes can take various forms: “hole burning” is the removal of material (typically a thin film of tellurium) by evaporation, melting or spalling — sometime s referred to as laser ablation; bubble or pit formation involves deformation of the surface, usually of a polymer overcoat on a metal reflector.