真乄科技業的頂尖投資團隊

C. RIOS ET AL., NATURE PHOTONICS, ADVANCE ONLINE PUBLICATION (2015)

Intense light pulses (pink) write data in a patch of GST, which can be read out as digital 1s and 0s with lower intensity light (red).

根據國外媒體報導，日前已經有研究人員創造出了首個光學存儲芯片，可以用來永久保存數據，而這個成果將可以讓SSD固態硬盤裡的數據更加安全。目前非易失存儲器所使用的電子芯片由於熱量和阻力的因素會產生限速，而光學存儲介質從目前來看就不會遇到這樣的問題。

目前，光學存儲芯片由IBM公司發明，並且旨在解決永久性的數據保存問題。而來自牛津大學和德國卡爾斯魯厄理工學院的研究團隊旨在通過我們熟悉的一種光學存儲媒介解決這個問題，而這個光學存儲媒介就是我們熟悉的DVD。

擁有重複燒錄功能的DVD和CD等存儲數據使用了一種名為GST的材質，一種由鍺、碲和銻等技術組成的混合元素，並且在激光的作用下可以改變結構。目前，來自英國和德國的團隊使用了波導​​技術加工了芯片，將光通過渠道蝕刻成一種合成材料。而這種芯片圖上了納米級的GST材質，然後通過高強度激光進行渠道蝕刻。 GST可以將原來的晶體機構變成非晶態結構，然後通過另一種低強度激光來檢測以及讀取數據。

GST可以重新將其轉化為晶體狀態，變成一個可以真正重寫的光盤媒介。而通過改變激光的波長和強度，研究團隊甚至可以在同一個位置保存高達8位數的數據，而這在二進制的電子設備中是一個巨大的進步。

Today’s electronic computer chips work at blazing speeds. But an alternate version that stores, manipulates, and moves data with photons of light instead of electrons would make today’s chips look like proverbial horses and buggies. Now, one team of researchers reports that it has created the first permanent optical memory on a chip, a critical step in that direction.

“I am very positive about the work,” says Valerio Pruneri, a laser physicist at the Institute of Photonic Sciences in Barcelona, Spain, who was not involved in the research. “It’s a great demonstration of a new concept.”

Interest in so-called photonic chips goes back decades, and it’s easy to see why. When electrons move through the basic parts of a computer chip—logic circuits that manipulate data, memory circuits that store it, and metal wires that ferry it along—they bump into one another, slowing down and generating heat that must be siphoned away. That’s not the case with photons, which travel together with no resistance, and do so at, well, light speed. Researchers have already made photon-friendly chips, with optical lines that replace metal wires and optical memory circuits. But the parts have some serious drawbacks. The memory circuits, for example, can store data only if they have a steady supply of power. When the power is turned off, the data disappear, too.

Now, researchers led by Harish Bhaskaran, a nanoengineering expert at the University of Oxford in the United Kingdom, and electrical engineer Wolfram Pernice at the Karlsruhe Institute of Technology in Germany, have hit on a solution to the disappearing memory problem using a material at the heart of rewritable CDs and DVDs. That material—abbreviated GST—consists of a thin layer of an alloy of germanium, antimony, and tellurium. When zapped with an intense pulse of laser light, GST film changes its atomic structure from an ordered crystalline lattice to an “amorphous” jumble. These two structures reflect light in different ways, and CDs and DVDs use this difference to store data. To read out the data—stored as patterns of tiny spots with a crystalline or amorphous order—a CD or DVD drive shines low-intensity laser light on a disk and tracks the way the light bounces off.

In their work with GST, the researchers noticed that the material affected not only how light reflects off the film, but also how much of it is absorbed. When a transparent material lay underneath the GST film, spots with a crystalline order absorbed more light than did spots with an amorphous structure.  

Next, the researchers wanted to see whether they could use this property to permanently store data on a chip and later read it out. To do so, they used standard chipmaking technology to outfit a chip with a silicon nitride device, known as a waveguide, which contains and channels pulses of light. They then placed a nanoscale patch of GST atop this waveguide. To write data in this layer, the scientists piped an intense pulse of light into the waveguide. The high intensity of the light’s electromagnetic field melted the GST, turning its crystalline atomic structure amorphous. A second, slightly less intense pulse could then cause the material to revert back to its original crystalline structure.

When the researchers wanted to read the data, they beamed in less intense pulses of light and measured how much light was transmitted through the waveguide. If little light was absorbed, they knew their data spot on the GST had an amorphous order; if more was absorbed, that meant it was crystalline.

Bhaskaran, Pernice, and their colleagues also took steps to dramatically increase the amount of data they could store and read. For starters, they sent multiple wavelengths of light through the waveguide at the same time, allowing them to write and read multiple bits of data simultaneously, something you can’t do with electrical data storage devices. And, as they report this week in Nature Photonics, by varying the intensity of their data-writing pulses, they were also able to control how much of each GST patch turned crystalline or amorphous at any one time. With this method, they could make one patch 90% amorphous but just 10% crystalline, and another 80% amorphous and 20% crystalline. That made it possible to store data in eight different such combinations, not just the usual binary 1s and 0s that would be used for 100% amorphous or crystalline spots. This dramatically boosts the amount of data each spot can store, Bhaskaran says.

Photonic memories still have a long way to go if they ever hope to catch up to their electronic counterparts. At a minimum, their storage density will have to climb orders of magnitude to be competitive. Ultimately, Bhaskaran says, if a more advanced photonic memory can be integrated with photonic logic and interconnections, the resulting chips have the potential to run at 50 to 100 times the speed of today’s computer processors.