Site: Matsushita Electric Industrial Co., Ltd.
Optical Disk Systems Development Center (ODSC)
3-1-1, Yagumo Nakamachi, Moriguchi City
Osaka, 570-8501, Japan
Date Visited 13 March 1998
Matsushita Electric Industrial Co., Ltd. (MEI), the number two consumer electronics company in Japan, is the leader of a group of more than 200 affiliates that serve business, industry, and consumer markets. It is best known for products that are marketed under the National, Panasonic, Quasar and Technics brands. FY 97 revenue of $61.0 billion was reported.
MEI has been a leader in optical storage, having released one of the first PD-compatible rewritable systems in 1995, and undertook a leading role in the development of DVD. The 21/2-hour meeting with the WTEC team consisted of three talks by MEI engineers with about 45 minutes for discussion between presentations.
Dr. Ohta began with a talk describing rewritable optical discs using phase change technology (which MEI has worked with since 1972). In comparison with magneto-optic recording, phase change (PC) has many advantages, including signals that are 20 times larger than MO (normalized for reflectivity), wide wavelength response (large signals over at least 430 to 830 nm), a simpler read and write optical system, and easier compatibility with DVD and CD read-only discs. PC media has a 50-year stability and can be overwritten more than 1 million times.
A key issue for near term DVD-RAM includes optimized thermal designs for higher sensitivity. Also, the need for unified DVD-RAM standards was described. A single standard is needed to maximize viability of the format.
During discussion, it was expected that recording densities of 120 mm diameter discs will reach 11 Gb/in2 using 0.6 NA optics if a blue (425 nm) laser is available. MEI recently announced an SHG laser that provides 26 mW at 425 nm, and that should cost only 10% more than a comparable laser diode. If a blue laser is not available, solid immersion lens (SIL) technology can be used to read high data densities; improving density using the same NA is desired, though, since more generations of discs will remain compatible.
Formats will migrate from 4.7 GB discs to double layer 8.5 GB, and then to 15 GB discs for HDTV recording. Single layer recording may achieve 20 GB or more by using higher NA, media superresolution, and thinner substrates. Beyond that, multilayer stacks, possibly up to 4 layers, can increase disc capacity.
Dr. Ohta's concluding remark that "phase-change welcomes nanometer memory technologies" was exemplified by Dr. Yokoyama's presentation on AFM recording. Marks of 10 nm diameter (~1 Tb/in2) with up to 100 times conductivity increases were recorded in GST films using 3 V pulses for 5 ms from a conductive AFM tip. Data are read with the AFM tip at 0.5 V with a few nA of current, and marks could be erased by reversing the pulsed voltage. Data rate is limited by the decreasing reliability of writing as pulse duration decreases but approached 1 kb/s in the demonstration.
Dr. Ishida described a high density magnetic tape recording system based on obliquely oriented metal evaporated tapes. His research goal is a 1 Gb/in2 product by the year 2000, using 5 ktpi track density and 200 kfrpi linear recording density. A demonstration of 1 Gb/in2 recording with 50 dB carrier-to-noise (by using an MIG type inductive head) was described.
The obliquely oriented Co-O tapes show potential beyond several Gb/in2, but signal-to-noise challenges remain. Applying more sensitive magneto-resistive heads in (helical scanning) removable tape systems requires significant innovation since they cannot survive contact recording. Furthermore, tape - head spacing for contact recording will be larger than HDD fly heights because of the relatively large separations that tape systems must accommodate (~30 nm protrusion height, 10 nm protective layer, [20 nm head recess] and ~ 20 nm for adhering impurities ["brown stain"]). Ultimately, if MR heads are used, tape properties must be re-optimized, and this work is underway. Tracking is also an issue; for higher density, tape thicknesses of 5 Ám are predicted, and expansion of polymer tapes (due to temperature or humidity) may cause excessive skew angle.
MEI is committed to rewritable discs based on phase change media. The resurgence of magneto-optical recording is considered to be an academic pursuit and not a viable path. The organization has a clear roadmap for disc products up to 15 GB or so, and company researchers believe multilayer technologies can push rewritable disc capacity to 80 GB.