Mock-ups incorporating Hoya's glass substrate. The right and left mock-ups use 10 0.5mm-thick glass substrates and nine 0.635mm-thick glass substrates, respectively.
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The capacity of HDDs is steadily increasing in preparation for the era in which the amount of data to be stored explodes. In the first half of 2017, Western Digital (WD) Corp and Seagate Technology LLC announced that they started volume production of 12-Tbyte 3.5-inch HDDs. And it is possible that the capacity of HDDs will increase by about 2 Tbytes per year and reach 20 Tbytes by 2020.

With the prospect of the era, Hoya Corp, which supplies glass substrates for HDDs in an exclusive way, is developing technologies with an ambition. Currently, glass substrates are used mainly for 2.5-inch HDDs that are designed for notebook computers, etc. The market for those HDDs is shrinking because they are being replaced with SSDs using NAND flash memory.

Nevertheless, Hoya expects that the demand for glass substrates will eventually start to increase and the scale of its glass substrate business will increase manyfold. The company considers that 3.5-inch HDDs, which currently use aluminum substrates, may start to employ glass substrates overnight as their capacity increases.

One of the advantages of glass substrates is that they have a higher rigidity than aluminum substrates and can be thinner than aluminum substrates, making it possible to increase the number of disks that can be stored in a case and increase the capacity. Hoya has already prototyped 0.5mm- and 0.381mm-thick substrates, enabling to house 10 and 12 substrates, respectively, in a 3.5-inch HDD whose thickness is about 1 inch.

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