Detecting and preventing the use of counterfeit electronic devices is a major imperative for both consumer and defense
electronics. Physically Unclonable Functions (PUFs) take advantage of small variations between each device that exist due to the
manufacturing process. The variations are not controllable, and thus are impossible to replicate. While PUFs based on
variations in electrical characteristics show promise, they suffer from temperature instability, complex circuit design, and
lack of implementation in non-CMOS devices.
A PUF based on variations in material properties, instead of electrical properties, overcomes the limitations of an
electrical PUF, but maintains the ability to incorporate a unique fingerprint during the manufacturing process. One of the
first processing steps in the wafer fabrication process is ion implantation. In this step, high energy ions bombard the
surface, creating localized defects that are later recrystallized upon thermal annealing. One attribute of the recrystallized
regions in silicon is that they can emit light when stimulated by a voltage or a light source such as a laser. As with all
wafer manufacturing processes, there are small variations that occur during the implantation and annealing process,
such as implant energy and dose, and anneal temperature. These variations in turn lead to variations in the light emitted,
creating unique optical fingerprints for each chip. Ion implantation is common for non-Si CMOS devices, such as GaAs
and GaN, making this optical fingerprint method applicable to other semiconductor platforms.
The material PUF seeks to overcome the limitations of the common electrical PUF, while maintaining the ease of
manufacturing by utilizing variations in standard wafer processing. The material PUF is a significantly simpler device
than the current electrical PUFs, requiring minimal design or additional processing. In order for the implanted regions to
emit light, a simple two-terminal device is all that is required to apply the operating voltage. In contrast, electrical PUFs
are based on architectures such as ring oscillators or arbiters, entailing the design of complex integrated circuits. The
material PUF also requires much less space on the chip, and could be implemented in unused space between circuits.
A second advantage is the ability to implement the material PFU in non Si-CMOS devices. For example, GaAs and GaN
wafers can be implanted with ions, such as erbium and europium, which lead to changes in the light emission properties
of the localized region. The ability to apply the material PUF concept to non-Si wafers is a significant benefit over the
A third improvement of the material PUF is the temperature stability of the device. The electrical PUFs suffer from
reliability and repeatability issues when subjected to temperatures over 150 C. This is because the CMOS circuits are
not rated above this temperature. In contrast, the material PUF is only limited by the temperature stability of the electrical
contacts to the implanted region. This makes the material PUF capable of stable and reliable operation under high
temperatures and other harsh environments.
The primary application for the material PUF will be in the microelectronics supply chain, both for defense and
commercial applications. For defense applications, it is a process that can be easily implemented at any wafer foundry,
and creates a more secure and trusted supply chain for critical programs. It can also be implemented in commercial
wafer foundries, reducing the threat of counterfeit components entering the marketplace.
- Ability to “finger print” a high volume commercially manufactured device, such as FPGAs, at the foundry, and
track throughout the supply chain
- Secure supply chain for application specific integrated circuits and RF devices used in defense programs
- Implementation for high volume consumer products such as controllers for brakes and air bags, or commercial