Stability & Longevity – Primary Goals
The materials and the write process used for the M-DISC were chosen with stability and longevity as the primary goals. These new materials enabled the use of a more durable data mark - a physical hole or pit that could be formed in the data layer. A much higher laser-power is used to write or create these physically changed pits in the data layer.
These physical pits have two main advantages over dye and phase-change-based optical media; |
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the permanent physical movement of the material and the permanent optical contrast between light and dark spots. Movement of the material actually enhances the edge of the mark as shown in the nearby scanning electron microscope image. The nanometer scale location of the edges is critical to the retention of data, with the enhanced edges further building-in longevity. The other advantage is the excellent, permanent optical contrast that comes from making a physical mark. The difference in optical quality between the pit, where there is no material, and the areas adjacent to the pit, where the material remains, provides a definite advantage in retention of data and in ease of reading the disc long into the future. Essentially, pits are better and allows for readable data even after hundreds of years.
Everyone Fails Except Millenniata
According to an independent report performed by the U.S. Department of Defense at China Lake, California, the M-DISC was the only optical disc
tested that did not suffer data failure. The discs from Mitsubishi, Verbatim, Taiyo Yuden, Delkin and MAM-A all failed. None of the data was recoverable after the exposure cycle. |
Millenniata
10 Errors
0% of discs failed |
Delkin
3284 Errors
100% of discs failed |
Verbatim
5000+ Errors
100% failed |
MAM-A
2096 Errors
100% of discs failed |
Taiyo Yuden (JVC)
4249 Errors
100% of discs failed |
Mitsubishi
5000+ Errors
100% of discs failed |
The Inorganic Data Layer
The patented data layer is composed entirely of inorganic materials and compounds including metals and metalloids. This layer is solid from room temperature to upwards of 500°C (932°F), and it is stable in the presence of oxygen, nitrogen, water, and other deleterious chemicals that may be found in ordinary storage environments.
Etching Data in Stone
The inorganic data layer materials undergo a physical change during the write process. When the data layer is irradiated by a focused laser, the intense heat generated causes the innermost layers to melt and to move away from the laser spot, creating a hole in the data layer as previously described. In contrast, the organic dyes used in typical DVD-recordable discs would merely decompose under the same thermal conditions.
Furthermore, when the melted portions of the M-DISC data layer cool after writing, the material surrounding the written voids forms a polycrystalline structure that is again reminiscent of the micro-crystalline structure of many common rocks.
Permanent by Design
The intent of the scientists and engineers who developed the M-DISC was to develop the modern, digital equivalent of engraving data, literally, in stone. The characteristics and features that enable a rock to survive for tens of thousands of years without a change were the inspiration behind the product. It isn't by chance that the M-DISC data layer is similar to a rock - it's by design!
Measuring for
Longevity
Measuring M-DISC performance to directly determine the longevity is a challenge. When something changes very slowly, taking meaningful measurements requires a long time. The data layer is so resistant to oxidation that observable changes in an M-DISC stored under normal conditions are still very small after weeks or months. One way to deal with this challenge is to make a worst-case estimate of the lifetime using well-known theories and data, then test the results against measured data to see if the estimate is useful.
Theorists agree that the oxidation of metals like those used in the M-DISC proceeds logarithmically. The bare metal forms a very thin, nano-scale oxide layer very quickly. This oxide layer then protects the rest of the metal layer from further oxidation. If this is the correct physical model for oxidation of the M-DISC data layer, the M-DISC reflectivity over time should look like the curve shown in Figure 1. Most of the change in reflectivity would occur in the first few months after the DISC is manufactured.
Greater than 10,000 Years
A worst-case scenario for failure in the data layer would be a critical loss in reflectivity as the metals in the M-DISC slowly oxidized. Failure would occur when the reflectivity dropped below the minimum specification of 18%. Figure 1 shows the reflectivity curve we would expect to see due to oxidation if the M-DISC data layers reach a reflectivity of 18% after 10,000 years. The curve shows that if the M-DISC was readable for only 10,000 years, we would expect to see an M-DISC lose more than 3% reflectivity after aging only 50 days. A 3% change is easily measureable. Of course, if the reflectivity changed at a slower rate, the M-DISC could be expected to last even longer. The actual observed reflectivity change is less than 1% after 300 to 350 days (as shown with the graph inset into Figure 1) indicating the actual performance of the M-DISC data layer is significantly better than our worst-case scenario. The comparison of the actual data to the 10,000-year example is very favorable. The obvious conclusion is the data on an M-DISC should be readable for greater than 10,000 years when stored in an ordinary, dry, room- temperature environment.
Polycarbonate: Stable for 1,000 Years
Since it is doubtful that the polycarbonate substrate materials can endure for that length of time, the substrate materials must be the actual weak link in the M-DISC structure. External studies conducted by the National Institute of Standards and Technology (NIST) concluded that the substrate materials in DVDs should be reliable for at least 1,000 years. Therefore, a lifetime estimate of at least 1,000 years, limited by the durability of the polycarbonate substrate, is very reasonable. |
