As system security demands continue to evolve, Physically Unclonable Functions (PUFs) are a promising solution for secure storage on Integrated Circuits (ICs). SRAM PUFs are among the most popular types of PUFs, since they require no additional circuitry and can be implemented with on-die memories such as caches and data memory that are readily available on both ASICs and FPGAs. This work demonstrates that SRAM PUFs are not well suited as PUFs, as they do not meet several requirements that constitute an ideal PUF. The compact nature of SRAM, standard interconnects and resiliency to environmental effects make SRAM PUFs particularly easy to clone. We consider several ways in which SRAM PUFs can be characterized and demonstrate a Focused Ion Beam circuit edit with which we were able to produce a physical clone of our Proof-of-Concept SRAM PUF implementation. As a result of the circuit edit, when challenged, the physical clone produced an identical physical response to the original device. To the best of our knowledge, this is the first work in which a physical clone of a Physically Unclonable Function was produced.

Cloning Physically Unclonable Functions

Optimizing focused ion beam created solid immersion lenses in bulk silicon using design of experiments

Solid immersion lenses (SILs) are shown to greatly enhance optical spatial resolution when measuring AlGaN/GaN High Electron Mobility Transistors (HEMTs), taking advantage of the high refractive index of the SiC substrates commonly used for these devices. Solid immersion lenses can be applied to techniques such as electroluminescence emission microscopy and Raman thermography, aiding the development device physics models. Focused ion beam milling is used to fabricate solid immersion lenses in SiC substrates with a numerical aperture of 1.3. A lateral spatial resolution of 300 nm is demonstrated at an emission wavelength of 700 nm, and an axial spatial resolution of 1.7 ± 0.3 μm at a laser wavelength of 532 nm is demonstrated; this is an improvement of 2.5× and 5×, respectively, when compared with a conventional 0.5 numerical aperture objective lens without a SIL. These results highlight the benefit of applying the solid immersion lenses technique to the optical characterization of GaN HEMTs. Further improvements may be gained through aberration compensation and increasing the SIL numerical aperture.

/pdf/solid-immersion-lenses-for-enhancing-the-optical-resolution-1qepex54bz.pdf

Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors

https://dl.asminternational.org/istfa/proceedings-pdf/ISTFA2011/38268/46/414276/istfa2011p0046.pdf

Instant Solid Immersion Lens Creation in Silicon with a Focused Ion Beam – Comparing Refractive and Diffractive Methods

This paper describes the development of a superzone solid immersion diffraction vortex lens and sub-wavelength antireflection surfaces for analyzing dense integrated circuitry through the silicon substrate. The diffractive optic is used with the scanning laser microscope imaging system at a wavelength of 1064 nm. The silicon substrate consists of wafer grade silicon, 1015 cm−3 P-type, with an integrated memory array at the 90 nm technology node as the target structures. The solid immersion diffractive optic is designed using computer generated holography, and the functionality is simulated using a finite difference time domain numerical method. The blazed phase profile and sub-wavelength structures of the diffractive optic are fabricated using a two step procedure of gray scale gallium implantation with the focused ion beam, followed by the reactive ion etching using CHF3 chemistry. The developed fabrication conditions for the optical structures investigate implant doses ranging from 0 to 1000 pC μm−2 using the 1000 pA beam current, with etch times from 0 to 25 min. Experimental results demonstrate functional optical vortex lenses that achieve selective suppression of signals from target IC structures to enhance the contrast of the surrounding circuitry. To reduce reflection losses, sub-wavelength, antireflection surfaces targeting the 1064 and 3300 nm wavelengths are investigated. Spatial periods of 140 and 500 nm are achieved, with fill factors of 0.3 to 0.4 over the quarter wavelength antireflective height. For resolution enhancement, a second order superzone solid immersion lens with a numerical aperture of 3.4 is fabricated and demonstrates a 1.6× improvement in image resolution over the first order solid immersion lens with a numerical aperture of 1.7, which in turn achieves a 3.5× improvement over no immersion lens.

Nanofabrication of superzone solid immersion vortex lens and subwavelength antireflection surfaces for enhanced scanning laser imaging

Creation of Solid Immersion Lenses in Bulk Silicon Using Focused Ion Beam Backside Editing Techniques

http://dl.asminternational.org/istfa/proceedings-pdf/doi/10.31399/asm.cp.istfa2009p0119/413867/istfa2009p0119.pdf

A Versatile Design of Solid Immersion Lenses in Bulk Silicon Using Focused Ion Beam Techniques

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Creation of Solid Immersion Lenses in Bulk Silicon Using Focused Ion Beam Backside Editing Techniques

A Versatile Design of Solid Immersion Lenses in Bulk Silicon Using Focused Ion Beam Techniques