Publication Date: 2014-Jan-10
The IP.com Prior Art Database
Disclosed is a ROM cell that resists reverse engineering.
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Because gaming chips are sold worldwide, there is a great risk of the chips being reverse engineered. One of the primary ways to reverse engineer a chip is to de-layer it and take photos of each of the layers. Because most ROM one and zero cells are visibly distinct, it is possible for hackers to view the contents of a ROM simply by taking a picture of the ROM at the correct metal layer. This can cause security issues, as the data held in the ROM is now literally visible and documentable.
In order to reduce this security issue, a visibility secure ROM cell must be created. This cell must be able to be programmed in a one and zero state without great visible differential between the two cells. In order to do this, the difference must be hidden from the top-down view and small enough that the effort to de-layer the chip will destroy the difference. To do this, one must create a ROM cell that differentiates between a one and a zero with the small oxide layer between a CA tower and a M1 hat. These two layers will be separated by a thin oxide layer that will either exist or not.
Even though these cells will be differentiable by cross-sectioning the chip, the cost in both parts and time increase greatly. Cross-sectioning a chip destroys the chip and is very error prone, increasing the cost of reverse engineering as well. Multiple cross sections will be required, and each cross section must hit the proper wordline whose location must be mapped from chip to chip...