Mehdi Anwar

Memristor PUF—A Security Primitive: Theory and Experiment

Physical unclonable functions (PUFs) have emerged as a promising hardware security primitive, but existing CMOS PUFs suffer from issues related to reliability and susceptibility to modeling attacks. Memristors, leveraging nanotechnology fabrication process and highly nonlinear behavior, pose as an interesting alternative. In this paper, we report the first demonstration of memristor based PUFs. The six memristors we fabricated show a 50% uncertainty of PUF response and high reliability upon repeated interrogation. A physics based circuit model of memristors was also implemented to accurately determine the simulation time required for randomly selected polyominoes from a 3-D array of memristors. The proposed model provides higher degree of complexity and results in seven orders of increase in simulation time for an attacker than that reported by Rajendran , 2012.

Memristor: Part I—The Underlying Physics and Conduction Mechanism

Memristor switching and observed I-V characteristics are explained using the underlying physics of the device in terms of the formation and rupture of filaments. Three different conduction mechanisms, namely-filament-assisted tunneling current, bulk tunneling current, and currents flowing through low and high conductivity filaments give rise to the total current in memristive systems. Heating of filaments during current conduction may reduce the ROFF/RON ratio of the device by increasing its ON resistance. In case of an organic layer, this issue can be circumvented by suitably increasing the organic layer thickness. Effects of different parameters on lifetime of memristors as resistance-switching random access memory have also been investigated.

Terahertz characterization of electronic components and comparison of terahertz imaging with x-ray imaging techniques

THz radiation is capable of penetrating most of nonmetallic materials and allows THz spectroscopy to be used to image the interior structures and constituent materials of wide variety of objects including Integrated circuits (ICs). The fact that many materials in THz spectral region have unique spectral fingerprints provides an authentication platform to distinguish between authentic and counterfeit electronic components. Counterfeit and authentic ICs are investigated using a high-speed terahertz spectrometer with laser pulse duration of 90 fs and repetition rate of 250 MHz with spectral range up to 3 THz. Time delays, refractive indices and absorption characteristics are extracted to distinguish between authentic and counterfeit parts. Spot measurements are used to develop THz imaging techniques. In this work it was observed that the packaging of counterfeit ICs, compared to their authentic counterparts, are not made from homogeneous materials. Moreover, THz techniques were used to observe different layers of the electronic components to inspect die and lead geometries. Considerable differences between the geometries of the dies/leads of the counterfeit ICs and their authentic counterparts were observed. Observing the different layers made it possible to distinguish blacktopped counterfeit ICs precisely. According to the best knowledge of authors the reported THz inspection techniques in this paper are reported for the first time for authentication of electronic components. Wide varieties of techniques such as X-ray tomography, scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and optical inspections using a high resolution microscope have also been being employed for detection of counterfeit ICs. In this paper, the achieved data from THz material inspections/ THz imaging are compared to the obtained results from other techniques to show excellent correlation. Compared to other techniques, THz inspection techniques have the privilege to be nondestructive, nonhazardous, less human dependent and fast.

Memristor: Part II–DC, Transient, and RF Analysis

The dc and RF circuit performance of memristor circuits, including transient behavior, is developed by considering current contributions arising from different conduction mechanisms, namely, filament-assisted and bulk tunneling currents and currents flowing through low and high conductivity filaments. The dc circuit model explains the observed I-V hysteresis and most importantly allows scaling and optimization. A transient circuit model of memristive system is developed, based upon the dynamics, incorporating underlying electrochemistry that suggests SET and RESET transitions for a 50-nm TiO2-based memristor take approximately 120 ps to stabilize. A faster READ/WRITE operation would require appropriate conditioning circuitry. RF analysis suggests for a maximum allowable frequency of 7.5 GHz beyond which memristors can no longer be used as RRAM. These values can be pushed to higher limits by increasing the device cross-sectional area or choosing lower permittivity materials. The developed model allows its incorporation in commercial circuit simulators. The derived model is validated by incorporating it in Chuas chaotic circuit.

Advanced terahertz techniques for quality control and counterfeit detection

This paper reports our invented methods for detection of counterfeit electronic. These versatile techniques are also handy in quality control applications. Terahertz pulsed laser systems are capable of giving the material characteristics and thus make it possible to distinguish between the materials used in authentic components and their counterfeit clones. Components with material defects can also be distinguished in section in this manner. In this work different refractive indices and absorption coefficients were observed for counterfeit components compared to their authentic counterparts. Existence of unexpected ingredient materials was detected in counterfeit components by Fourier Transform analysis of the transmitted terahertz pulse. Thicknesses of different layers are obtainable by analyzing the reflected terahertz pulse. Existence of unexpected layers is also detectable in this manner. Recycled, sanded and blacktopped counterfeit electronic components were detected as a result of these analyses. Counterfeit ICs with die dislocations were detected by depicting the terahertz raster scanning data in a coordinate plane which gives terahertz images. In the same manner, raster scanning of the reflected pulse gives terahertz images of the surfaces of the components which were used to investigate contaminant materials and sanded points on the surfaces. The results of the later technique, reveals the recycled counterfeit components.

Developing terahertz imaging equation and enhancement of the resolution of terahertz images using deconvolution

This paper introduces a novel reconstruction approach for enhancing the resolution of the terahertz (THz) images. For this purpose the THz imaging equation is derived. According to our best knowledge we are reporting the first THz imaging equation by this paper. This imaging equation is universal for THz far-field imaging systems and can be used for analyzing, describing and modeling of these systems. The geometry and behavior of Gaussian beams in far-field region imply that the FWHM of the THz beams diverge as the frequencies of the beams decrease. Thus, the resolution of the measurement decreases in lower frequencies. On the other hand, the depth of penetration of THz beams decreases as frequency increases. Roughly speaking beams in sub 1.5 THz, are transmitted into integrated circuit (IC) packages and the similar packaged objects. Thus, it is not possible to use the THz pulse with higher frequencies in order to achieve higher resolution inspection of packaged items. In this paper, after developing the 3-D THz point spread function (PSF) of the scanning THz beam and then the THz imaging equation, THz images are enhanced through deconvolution of the THz PSF and THz images. As a result, the resolution has been improved several times beyond the physical limitations of the THz measurement setup in the far-field region and sub-Nyquist images have been achieved. Particularly, MSE and SSIM´ have been increased by 27% and 50% respectively. Details as small as 0.2 mm were made visible in the THz images which originally reveals no details smaller than 2.2 mm. In other words the resolution of the images has been increased by 10 times. The accuracy of the reconstructed images was proved by high resolution X-ray images.

Modeling of terahertz images based on x-ray images: a novel approach for verification of terahertz images and identification of objects with fine details beyond terahertz resolution

In this work, terahertz images have been simulated from X-ray images. For this aim the terahertz raster scanning process is modeled by a two dimensional convolution of the modelled THz beam and the X-ray image. The mathematical model of the terahertz beam has been modeled by a Gaussian function. The variables in this function are frequency of the beam, lateral location and absorption coefficient of the object. The accuracy of the proposed approach has been verified by comparing the results with the actual terahertz images.

A survey on GaN- based devices for terahertz photonics

With fast growing of the photonics and power electronic systems, the need for high power- high frequency semiconductor devices is sensed tremendously. GaN provides the highest electron saturation velocity, breakdown voltage and operation temperature, and thus combined frequency-power performance among commonly used semiconductors. With achieving the first THz image in just two decades ago, generation and detection of terahertz (THz) radiation is one of the most emerging photonic areas. The industrial needs for compact, economical, high resolution and high power THz imaging and spectroscopy systems are fueling the utilization of GaN for the realizing of the next generation of THz systems. As it is reviewed in this paper, the mentioned characteristics of GaN together with its capabilities of providing high 2-dimentional election densities and large longitudinal-optical phonon of ~90 meV, make it one of the most promising semiconductor materials for the future of the THz generation, detection, mixing, and frequency multiplication. GaN- based devices have shown capabilities of operating in the upper THz frequency band of 5- 12 THz with relatively high photon densities and in room temperature. As a result, THz imaging and spectroscopy systems with high resolutions and depths of penetrations can be realized via utilizing GaN- based devices. In this paper, a comprehensive review on the history and state of the art of the GaN- based electronic devices, including plasma HFETs, NDRs, HDSDs, IMPATTs, QCLs, HEMTs, Gunn diodes and TeraFETs together with their impact on the future of THz imaging and spectroscopy systems is provided.

Active layer design and power calculation of nitride-based THz quantum cascade lasers

Room temperature III-nitride QCL THz is reported. With increasing carrier concentration, the peak in optical shifts towards higher energies. Peak in the optical gain increases with carrier concentration demonstrating a blue shift correlated to quantum confinement. THz power increases linearly with current demonstrating an output power of 0.4448 μW at 6THz. A higher THz power is obtained in AlxGa1-xN/GaN/AlxGa1-x heterostructures as compared to heterostructures incorporating In. An increase in the Al-mole fraction results in higher THz power.

Active layer design of THz GaN quantum cascade lasers

The structural, material and field dependence of the THz lasing frequency is reported for a QCL based upon GaN/AlGaN heterostructures. The inter-subband transition initiated generation of THz followed by the LO-phonon assisted fast depopulation takes into account the appropriate energy band alignments. Valence and conduction band alignments incorporating spin-orbit and crystal field splitting as well as bi-axial strain are used to determine the conduction band offset as a function of Al-mole fraction. Determination of eigen states takes into account the spontaneous and piezoelectric polarization induced modification in the conduction band profile. A lower THz generation frequency is predicted for Ga-face GaN/AlGaN-based QCLs using the revised energy band alignments.