Kiarash Ahi

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.

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.

Review of GaN-based devices for terahertz operation

Abstract. GaN provides the highest electron saturation velocity, breakdown voltage, operation temperature, and thus the highest combined frequency-power performance among commonly used semiconductors. The industrial need for compact, economical, high-resolution, and high-power terahertz (THz) imaging and spectroscopy systems are promoting the utilization of GaN for implementing the next generation of THz systems. As it is reviewed, the mentioned characteristics of GaN together with its capabilities of providing high two-dimensional 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 emitters, detectors, mixers, and frequency multiplicators. GaN-based devices have shown capabilities of operation in the upper THz frequency band of 5 to 12 THz with relatively high photon densities in room temperature. As a result, THz imaging and spectroscopy systems with high resolution and deep depth of penetration can be realized through utilizing GaN-based devices. A comprehensive review of the history and the state of the art of GaN-based electronic devices, including plasma heterostructure field-effect transistors, negative differential resistances, hetero-dimensional Schottky diodes, impact avalanche transit times, quantum-cascade lasers, high electron mobility transistors, Gunn diodes, and tera field-effect transistors together with their impact on the future of THz imaging and spectroscopy systems is provided.

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.

Encrypted Electron Beam Lithography Nano-Signatures for Authentication

In this work, engineered nanostructures (ENS) have been fabricated on the packed integrated circuits. Coding lookup tables were developed to assign different digits in numerical matrices to different fabricated nano-signatures. The numerical matrices are encrypted according to advanced encryption standard (AES). The encrypted numerical matrix is ink printed on the components, and the nanosignatures are fabricated on the packaged of the chips via electron beam lithography (EBL). This process is to be done in the manufacturer side of the supply chain. The numerical matrix and the nanosignature accompany the product in its long journey in the global supply chain. The global supply chain is proved to be susceptible to counterfeiters. For keeping counterfeiters‘ hands out of the process, the cipher key and the coding lookup tables are provided to the consumer using a secure direct line between the authentic manufacturer and the consumer. In the consumer side, the printed numerical matrix is decrypted. Having the decrypted numerical matrix makes it possible to extract the nanosignature from the laser speckle pattern shined on the packaged product. In this work, an algorithm is developed to extract the nano-signature by having the decrypted matrix and reflected laser speckle patterns as inputs. Confirming the existence of the nano-signature confirms the authenticity of the component. Imitating the nano-signatures by the counterfeiters is not possible because there is no way for them to observe the shape of these signatures without having access to the cipher key.

Fabrication of Robust Nano-Signatures for Identification of Authentic Electronic Components and Counterfeit Avoidance

In this paper, a novel approach for marking integrated circuit packages with authentication nanosignatures is introduced. In this work, the signatures patterns are fabricated using electron beam lithography. Moreover, the robustness of these signatures against aging and humidity is investigated. A recipe comprising image processing techniques and measurement of similarity indices has been developed. These signatures are proposed to be fabricated at the manufacturer side of the supply chain. Then, they are decoded at the consumer end. Thus, robustness against ambient environment and aging is a requirement for these signatures to survive in the global supply chain. Calculated Mean Square Error and Structural SIMilarity Index confirmed that the reflected patterns of the signatures remain unchanged against aging and humidity.

A memristor-based compressive sensing architecture

Memristors are considered as one promising candidate for future memory and computing fabrics. However, the design of memristor-based circuits is under a critical challenge of inevitable variations due to non-ideal fabrication processes and the resulted performance uncertainties. This kind of randomness can be utilized in many other applications, such as compressive sensing based data acquisition, which is conducted by a random sensing matrix. Existing compressive sensing systems are usually implemented in digital CMOS circuits, which suffer the problems of high hardware complexity and limited sampling speed. In this paper, we exploit the inherent variations in memristor devices to generate random sensing matrices for compressive sensing and achieve low cost and high performance operations. Simulation results demonstrate the advantages of the proposed memristor-based compressive sensing architecture.

Growth dependent optical properties of ZnMgO at THz frequencies

A relatively high Mg mole fraction of 7% is achieved using the cavitation effect under sonication to overcome the low solubility of ZnO-MgO at low temperature. The Mg mole fraction is confirmed by shift in the near band emission of free exciton under photoluminescence spectroscopy at room temperature. The x-ray diffraction pattern has a large peak associated to ZnO (002) from which the c-lattice constant is calculated to be 5.1967Ǻ. The nanorods (NRs) grown via sonochemical are compared to nanowires (NWs) grown using metal organic chemical vapor deposition (MOCVD) and hydrothermal synthesis. Also, the effect of the ZnO film used as seed layer is described and compare to a simple spin coated layer. Terahertz (THz) index of refraction and dielectric constant of wurtzite Zn1-xMgxO NWs with Mg mole fraction of 7% via sonochemical are determined using THz time domain spectroscopy (THz-TDS). The results are compared with ZnO and ZnMgO NWs with 10% Mg mole fraction grown using MOCVD. The successful growth of Zn1-xMgxO with wurtzite structure at low temperature permits realization of the growth of heterostructures, quantum well, nanowires and nanorods on flexible substrates providing lower cost, optical and carrier confinement necessary in advanced light emitting diodes (LEDs), laser diodes (LDs) and high efficiency solar cells.