Ovonic Unified Memory Technical Presentation
Ovonyx is developing a microelectronics memory technology called OUM that uses unique thin-film materials to store information economically and with excellent solid-state memory properties. The thin-film material is a phase-change chalcogenide alloy similar to the film used to store information on commercial CD-RW and DVD-RAM optical disks, based on proprietary technology originally developed by and exclusively licensed from Energy Conversion Devices, Inc.
Typical Phase Change Alloy
Optical memory disks use laser light to write small spots by converting the thin film back and forth from amorphous (disordered atomic structure) to crystalline (regular, highly repetitive, and ordered atomic structure). The digital data of 1s and 0s are stored as amorphous (high resistance and non-reflective) or crystalline (low resistance and reflective) structures. OUM devices store data in a similar manner but use electrical energy controlled by small transistors to electronically convert the material to crystalline or to amorphous (thus a 1 or a 0). This electronic solid-state memory stores data in a much smaller area and with higher speeds for both read and write than its optical counterpart.
The OUM solid-state memory has cost advantages over conventional solid-state memories such as DRAM or Flash due to its thin-film nature, very small active storage media, and simple device structure. OUM requires fewer steps in an IC manufacturing process resulting in reduced cycle times, fewer defects, and greater manufacturing flexibility. Smaller storage area and cell volume result in smaller die sizes without the increasingly exaggerated topologies, thereby producing more memory circuits per wafer with a process that deviates little from a basic CMOS logic flow.
Performance of the OUM memory cell provides for near ideal memory properties. The memory storage is nonvolatile (information is retained without power applied). A computer using OUM could be turned off and then turned back on immediately or 10 years later and start right up where the user left off. These OUM computers would not be subject to critical data loss when the system hangs up or when power is abruptly lost as are present day computers using DRAM and/or SRAM. With “instant on” operation, OUM computer users would not have to wait for the system to boot up and reload DRAM (presently several minutes are required after power-on where nothing useful is done). Using an OUM memory with no power required to maintain memory while operating or in standby provides substantial competitive advantages for portable applications where battery size and operating time between charging are key competitive metrics.
Adding to the cell’s attractiveness, the operating speed of OUM memory technology is similar to DRAM and many orders of magnitude faster than Flash write. Also, unlike conventional Flash memory, OUM memory is fully random accessible for memory addressing. Any given bit can be uniquely addressed and then written or read by the customer. Further, Flash memory “wears out” (fails) after 100,000 write cycles, while the OUM memory state can be written more than 10 trillion times, making this memory useful for program storage (Flash) as well as general purpose interactive (DRAM) data storage memory.
The small size, flat topology, and low voltage operation make OUM memory technology highly scalable to smaller geometries. Cell performance improves with shrinking, avoiding many of the scaling barriers arising in conventional charge-based DRAM and Flash technologies. For example, DRAM-based memories need a fixed amount of surface area to store the necessary amount of charge, resulting in undesirable tall skinny structures like a city skyline. This radical topography adds cost, complexity, and cycle time to a conventional DRAM memory process. Also enabling shrinking, the OUM memory provides higher speed active read current from its thin-film memory media, avoiding the fixed charge read approach of a DRAM with related test, noise, and soft-error problems.
OUM has direct application in all products presently using solid-state memory. These would include computers (desktop, laptop, and palm), cell phones, graphics-3D rendering, GPS, video conferencing, multi-media, Internet networking and interfacing, entertainment, digital TV, telecom, PDA, digital voice recorders, modems, DVD, networking (ATM), Ethernet, and pagers. Furthermore, the relatively simple cell structure and process with its advantageous memory properties make this technology well suited for providing embedded memory on logic ICs where on-board memory can provide significant product performance advantages. OUM offers a way to realize full system-on-a-chip capability through integrating unified memory, linear, and logic on the same silicon chip.