Farahiyah Mustafa

Dual-Functional On-Chip AlGaAs/GaAs Schottky Diode for RF Power Detection and Low-Power Rectenna Applications

A Schottky diode has been designed and fabricated on an n-AlGaAs/GaAs high-electron-mobility-transistor (HEMT) structure. Current-voltage (I–V) measurements show good device rectification, with a Schottky barrier height of 0.4349 eV for Ni/Au metallization. The differences between the Schottky barrier height and the theoretical value (1.443 eV) are due to the fabrication process and smaller contact area. The RF signals up to 1 GHz are rectified well by the fabricated Schottky diode and a stable DC output voltage is obtained. The increment ratio of output voltage vs input power is 0.2 V/dBm for all tested frequencies, which is considered good enough for RF power detection. Power conversion efficiency up to 50% is obtained at frequency of 1 GHz and input power of 20 dBm with series connection between diode and load, which also shows the device’s good potential as a rectenna device with further improvement. The fabricated n-AlGaAs/GaAs Schottky diode thus provides a conduit for breakthrough designs for RF power detectors, as well as ultra-low power on-chip rectenna device technology to be integrated in nanosystems.

Generalized 3D transverse magnetic mode method for analysis of interaction between drifting plasma waves in 2DEG-structured semiconductors and electromagnetic space harmonic waves

Up to now, the terahertz (THz) band is still an unexplored region in the sense that no practical application exists. New operating principles by traveling wave concept should be, therefore, appreciated for the real applications. In this paper, the generalized three-dimensional (3D) transverse magnetic (TM) mode analysis to analyze the characteristics of two-dimensional electron gas (2DEG) drifting plasma at the III-V high-electron-mobility-transistor (HEMT) hetero-interface such as AlGaAs/GaAs hetero-interface and its interaction with propagating electromagnetic space harmonic wave is presented. It includes, (1) the determination of electromagnetic flelds in semiconductor drifting plasma using the combination of well-known Maxwells equations and carrier kinetic equation based on semiconductor ∞uid model and the derivation of the efiective permittivity of drifting plasma in 2DEG on semi-insulating substrate, and (2) the analysis to describe the presence of interactions using a so-called interdigital-gated HEMT plasma wave devices. To describe the interaction, the admittance of the interdigital gate is evaluated. The numerical procedures to solve the integral equations which are used in determining the admittance is explained. A negative conductance is obtained when drifting carrier velocity is slightly exceed the fundamental wave velocity indicates the signiflcant condition of the interaction. A brief analysis and discussion on the Dyakonov-Shur THz surface wave in 2DEG is also presented.

RF-DC power conversion of Schottky diode fabricated on AlGaAs/GaAs heterostructure for on-chip rectenna device application in nanosystem

The Schottky diodes enjoined with coplanar waveguides are investigated for applications in on-chip rectenna device application without insertion of a matching circuit. The design, fabrication, DC characteristics and RF-to-DC conversion of the AlGaAs/GaAs HEMT Schottky diode is presented. The RF signals are well converted by the fabricated Schottky diodes with cut-off frequency up to 20 GHz estimated in direct injection experiments. The outcomes of these results provide conduit for breakthrough designs for ultra-low power on-chip rectenna device technology to be integrated in nanosystems.

RF characterization of planar dipole antenna for on-chip integration with GaAs-based schottky diode

The design and RF characteristics of planar dipole antenna facilitated with coplanar waveguide structure was presented. The dipole antennas were fabricated on semi-insulated GaAs substrates by using standard photolithography and lift-off process. As expected, it can be seen that the fundamental resonant frequency shift to higher frequency when the length of antenna decreases. Interestingly, the resonant frequencies of antenna are almost unchanged with the variation of antenna width and metal thickness. The width of dipole antenna and metal thickness only has an effect on the magnitude of return loss where the magnitude increases to more negative value with the increase of width and decrease of metal thickness. One of the most promising applications of our proposed dipole antenna is the capability to be integrated directly with AlGaAs/GaAs Schottky diode without any insertion of matching circuit between them.

Fabrication and Characterization of Planar Dipole Antenna Integrated with GaAs Based-Schottky Diode for On-chip Electronic Device Application

The design and RF characteristics of planar dipole antennas facilitated with coplanar waveguide (CPW) structure on semi-insulated GaAs are performed and confirmed to work in super high frequency (SHF) range. As expected, the fundamental resonant frequency shifts to higher frequency when the length of antenna decreases. Interestingly, the resonant frequencies of antenna are almost unchanged with the variation of antenna width and metal thickness. It is shown experimentally that return loss down to −54 dB with a metal thickness of 50 nm is obtainable. Preliminary investigation on design, fabrication, and DC and RF characteristics of the integrated device (planar dipole antenna + Schottky diode) on AlGaAs/GaAs HEMT structure is presented. From the preliminary direct irradiation experiments using the integrated device, the Schottky diode is not turned on due to weak reception of RF signal by dipole antenna. Further extensive considerations on the polarization of irradiation etc. need to be carried out in order to improve the signal reception. These preliminary results provide a new breakthrough for on-chip electronic device application in nanosystems.

Fabrication and Characterization of GaN-Based Two Terminal Devices for Liquid Sensing

Gallium Nitride (GaN) based materials are highly suitable for liquid-phase sensor applications due to their chemical stability and high internal piezoelectric polarization. The sensitivity of GaN surfaces in aqueous solutions and polar liquids has been investigated. For this purpose, two terminal devices fabricated on bulk Si doped-GaN structures and undoped-AlGaN/GaN heterostructures with unpassivated open area are used to measure the responses to the changes of the H+ concentration in aqueous solutions and the dipole moment in polar liquids. The I–V characteristics show that the devices are able to distinguish the variations of pH. It is observed that the drain current decreases linearly with pH for both device structures. Evaluating the sensitivity in aqueous solutions at VDS = 2V, a quite large current change is obtained for both structures. For the response to polar liquids, it is also found that the drain current decreases with the dipole moments. The results indicate that both devices are capable of distinguishing molecules with different dipole moments.

RF-to-DC Characteristics of Direct Irradiated On-Chip Gallium Arsenide Schottky Diode and Antenna for Application in Proximity Communication System

We report the RF-to-DC characteristics of the integrated AlGaAs/GaAs Schottky diode and antenna under the direct injection and irradiation condition. The conversion efficiency up to 80% under direct injection of 1 GHz signal to the diode was achieved. It was found that the reduction of series resistance and parallel connection of diode and load tend to lead to the improvement of RF-to-DC conversion efficiency. Under direct irradiation from antenna-to-antenna method, the output voltage of 35 mV was still obtainable for the distance of 8 cm between both antennas in spite of large mismatch in the resonant frequency between the diode and the connected antenna. Higher output voltage in volt range is expected to be achievable for the well-matching condition. The proposed on-chip AlGaAs/GaAs HEMT Schottky diode and antenna seems to be a promising candidate to be used for application in proximity communication system as a wireless low power source as well as a highly sensitive RF detector.

Power conversion efficiency of AlGaAs/GaAs Schottky diode for low-power on-chip rectenna device application

A Schottky diode has been designed and fabricated on n‐AlGaAs/GaAs high‐electron‐mobility‐transistor (HEMT) structure. Current‐voltage (I–V) measurements show good device rectification with a Schottky barrier height of 0.4349 eV for Ni/Au metallization. The differences of Schottky barrier height from theoretical value are due to the fabrication process and smaller contact area. The RF signals up to 1 GHz are well rectified by the fabricated Schottky diodes and stable DC output voltage is obtained. Power conversion efficiency up to 50% is obtained at 1 GHz with series connection between diode and load. The fabricated the n‐AlGaAs/GaAs Schottky diode provide conduit for breakthrough designs for ultra‐low power on‐chip rectenna device technology to be integrated in nanosystems.

Fabrication and Characterization of n-AlGaAs/GaAs Schottky Diode for Rectenna Device Application

Schottky diode was designed and fabricated on n-AlGaAs/GaAs high electron mobility transistor (HEMT) structure for rectenna device application. Rectenna is one of the most potential devices to form the wireless power supply which is really good at converting microwaves to DC. The processing steps used in the fabrication of Schottky diode were the conventional steps used in standard GaAs processing. Current-voltage (I–V) measurements showed that the device had rectifying properties with a barrier height of 0.5468 eV for Ni/Au metallization. The fabricated Schottky diode detected RF signals and the cut-off frequency up to 20 GHz was estimated in direct injection experiments. These preliminary results will provide a breakthrough for the direct integration with antenna towards realization of rectenna device application.

On-chip integration of planar dipole antenna with AlGaAs/GaAs Schottky diode for RF power detection

Recently, the concept of intelligent quantum (IQ) chip introduced by Hasegawa et al. [1] using III–V material as a base material where nanometer scale quantum processors and memories are integrated on chip with capabilities of wireless power supply, wireless communication circuit and various sensing functions, has been demonstrated. Schottky diode is a fast rectifying device [2] and can be used as RF power detector to detect damaging signal as well as rectenna device to supply DC power to the other on-chip devices. The design and fabrication of ultra-low power n-AlGaAs/GaAs high electron mobility transistor (HEMT) Schottky diode for on-chip RF power detector and rectenna are not extensively investigated.