Abdiel Rivera

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.

ZnMgO/ZnO Core-Shell Structures for Gas Sensing

Co-axial Zn1−xMgxO core, ZnO shell structures were grown using metal organic chemical vapor deposition (MOCVD), with Mg mole fractions of 2, 5 and 10%. The co-axial core shell structure, with the respective Mg concentration is verified using scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). The response times (ṟise time and fall time) of the devices, after being exposed to methanol, varied with Mg mole fraction at the core, r-0.17s and, f-0.37s & f-0.48s for 2% Mg, r-0.81s and, f-5.98s & f-0.89s for 5% Mg and r-0.33s and f-0.13s for 10% Mg. The sensitivity of the devices at room temperature increased with the increment of Mg mole fraction at the core, 25%, 48% and 50% with Mg concentration of 0.02, 0.05 and 0.1, respectively, under high concentration of methanol. The estimated activation energy, corresponds to doubly charged oxygen vacancy (Vo2+).

ZnMgO solar blind detectors: from material to systems

Zinc oxide (ZnO) is a unique wide bandgap biocompatible material system exhibiting both semiconducting and piezoelectric properties that has a diverse group of growth morphologies. Bulk ZnO has a bandgap of 3.37 eV that corresponds to emissions in the ultraviolet (UV) spectral band. Highly ordered vertical arrays of ZnO nanowires (NWs) have been grown on substrates including silicon, SiO2, GaN, and sapphire using a metal organic chemical vapor deposition (MOCVD) growth process. The structural and optical properties of the grown vertically aligned ZnO NW arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. Compared to conventional UV sensors, detectors based on ZnO NWs offer high UV sensitivity and low visible sensitivity, and are expected to exhibit low noise, high quantum efficiency, extended lifetimes, and have low power requirements. The photoresponse switching properties of NW array based sensing devices have been measured with intermittent exposure to UV radiation, where the devices were found to switch between low and high conductivity states at time intervals on the order of a few seconds. Envisioned applications for such sensors/FPAs potentially include threat detection and threat warning.

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.

Optimized Growth of ZnO Nanowires and Nanorods Using MOCVD

ZnO NWs were grown on Si (111) and Al2O3 substrates using MOCVD. ZnO (002) NWs on Si were randomly orientated while the NWs grown on sapphire were mostly vertically aligned as evident from scanning electron microscope images. The c-axis lattice constant corresponding to ZnO (002)/Si(111) demonstrated a dominant peak at 34.47°(2θ) attributed to ZnO along (002) with a FHWM of 0.0948°(θ) with corresponding c and a-lattice axes constants of 5.1996A and 3.2456A, respectively. The c-axis lattice constant for ZnO/sapphire was estimated to be 5.205A resulting in an out of plane strain of only 0.03%. Photoluminescence of ZnO nanowires grown on sapphire shows absorption peaks associated to exciton-exciton recombination and native defect such as zinc interstitial. In the case of NWs grown on Si, only exciton to exciton recombination was observed.

Energy Harvesting Leveraging Piezoelectric Property of ZnO Nanorods

Vertical ZnO nanorods (NRs) were grown on flexible plastic substrates at low temperature using hydrothermal synthesis method. An energy scavenging piezoelectric device was constructed using two flexible substrates with the NR sides facing each other providing a maximum open-circuit voltage of 1.4 V (peak). Two sets of three piezoelectric devices connected in series in a half-diode-bridge circuit configuration was demonstrated to turn on a commercial red LED.

ZnO nanowire growth and characterization for UV detection and imaging applications

Zinc oxide (ZnO) is a unique wide bandgap biocompatible material system exhibiting both semiconducting and piezoelectric properties that has a diverse group of growth morphologies. Bulk ZnO has a bandgap of 3.37 eV that corresponds to emissions in the ultraviolet (UV) spectral band. Highly ordered vertical arrays of ZnO nanowires (NWs) have been grown on substrates including silicon, SiO2, GaN, and sapphire using a metal organic chemical vapor deposition (MOCVD) growth process. The structural and optical properties of the grown vertically aligned ZnO NW arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. Compared to conventional UV sensors, detectors based on ZnO NWs offer high UV sensitivity and low visible sensitivity, and are expected to exhibit low noise, high quantum efficiency, extended lifetimes, and have low power requirements. The photoresponse switching properties of NW array based sensing devices have been measured with intermittent exposure to UV radiation, where the devices were found to switch between low and high conductivity states at time intervals on the order of a few seconds. Furthermore, NW based UV sensors and focal plane arrays (FPAs) show promise for imaging in the near marine boundary layer, an area extending up to about six meters above the ocean surface characterized by a relatively high degree of aerosols and turbulence. Envisioned applications for such sensors/FPAs potentially integrated into submarine photonic masts (which would maintain their effectiveness even in bright daylight conditions) include threat detection and threat warning.

MOCVD growth of ZnO nanowire arrays for advanced UV detectors

Zinc oxide (ZnO) is a biocompatible and versatile functional material having a bandgap of 3.37 eV that exhibits both semiconducting and piezoelectric properties and has a diverse group of growth morphologies. We have grown highly ordered vertical arrays of ZnO nanowires (NWs) using a metal organic chemical vapor deposition (MOCVD) growth process on various substrates. The NWs were grown on p-Si (100), SiO2, and m-plane sapphire substrates. The structural and optical properties of the grown vertically aligned ZnO NW arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. The unique diffraction pattern for ZnO (002) concurred with the SEM inspection indicating vertical orientation of the NWs. UV detectors based on ZnO NWs offer high UV sensitivity and low visible sensitivity for applications such as missile plume detection and threat warning. Compared to the photomultiplier tubes (PMTs) prevalent in current missile warning systems, the NW detector arrays are expected to exhibit low noise, extended lifetimes, and low power requirements for UV detector applications.

Growth and characterization of nanowires and nanorods on Al 2 O 3 (110), Si(111) and SiO 2 /p-Si(100) by MOCVD

We report growth of ZnO nanowires and nanorods using an atmospheric pressure, horizontal MOCVD, without any metal catalyst. The ZnO structures were grown on sapphire (110), Si(111) and SiO2/p-Si(111) substrates by controlling the ZnO precursor flow, growth temperature and distance from the injector. Prior to the growth of the nanostructure, a thin film of ZnO was grown at 400°C for 2 mins, DeZ was used as ZnO precursor with a flow rate of 200 sccm, N2O was used as oxygen source with a flow rate of 50 sccm and N2 was used as the carrier gas.