Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
With reference now to the figures, there is depicted a method and apparatus for providing a unique chip identification circuit 10 for an integrated circuit, which chip identification does not require specialized processing to create the unique identification for the integrated circuit, and which is stable and can be reliably read across repeated instances and a duration of time. In addition, the circuitry as described herein may also be used to produce a stable encryption key, and for other high security applications.
In basic concept, the circuitry 10 is added to each individual integrated circuit as a part of the mask set for the integrated circuits. Thus, as the integrated circuits are fabricated in wafer form, the circuit 10 is fabricated at the same time. Thus, no additional processing is required to fabricate the circuit 10.
The circuit 10 preferably has at least one property such the circuits 10 on different chips will produce at least one characteristic that is different from chip to chip, even though the circuit 10 on each of the different chips receives the same input.
Because of the similarities in the fabrication and design of the two transistors, it might be expected that they would have exactly the same voltage threshold. However, very subtle differences in the transistors typically arise such as by “chance” or other uncharacterized processing and material differences. Thus, there tends to be a measurable difference ΔV0 between the voltage thresholds Vt1 and Vt2. Depending upon which of the two voltage thresholds is greater than the other, this voltage difference can be interpreted as either a logical zero or a logical one from the bit cell 2. Practically speaking, the value of the bit cell 2, either zero or one, tends to be completely random from one integrated circuit to another.
Thus, by stringing together a given number of the bit cells 2—such as 128, 256, or some other number—a circuit 10, as depicted in
Unfortunately, some of the bit cells 2 have transistors with voltage thresholds Vt1 and Vt2 that are so close in value one to another, that the voltage differential ΔV0 is either so small that it cannot be reliably read, or actually flips back and forth in value from negative to positive (for example). Thus, such a bit cell 2, referred to as a soft cell that produces a soft bit, would tend to change its value in an unpredictable manner as it is read from time to time, thereby changing the value of the circuit 10. This tends to make the circuit 10 unreliable as a means for uniquely and repeatedly identifying the integrated circuit or producing an encryption key. Therefore, it is desirable to identify such soft cells 2 and remove them in some manner.
This same effect could be achieved using antifuse technology where the antifuse 6 as depicted in
The foregoing description of preferred embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.