Browsing by Subject "Threshold voltage"

Now showing 1 - 10 of 10

Open Access
2-nm laser-synthesized Si nanoparticles for low-power charge trapping memory devices
(IEEE, 2014-08) El-Atab, N.; Özcan, Ayşe; Alkış, Sabri; Okyay, Ali Kemal; Nayfeh, A.
In this work, the effect of embedding Silicon Nanoparticles (Si-NPs) in ZnO based charge trapping memory devices is studied. Si-NPs are fabricated by laser ablation of a silicon wafer in deionized water followed by sonication and filtration. The active layer of the memory was deposited by Atomic Layer Deposition (ALD) and spin coating technique was used to deliver the Si-NPs across the sample. The nanoparticles provided a good retention of charges (>10 years) in the memory cells and allowed for a large threshold voltage (Vt) shift (3.4 V) at reduced programming voltages (1 V). The addition of ZnO to the charge trapping media enhanced the electric field across the tunnel oxide and allowed for larger memory window at lower operating voltages. © 2014 IEEE.
Open Access
AlGaN/GaN HEMT-based fully monolithic X-band low noise amplifier
(Wiley, 2005-04) Schwindt, R.; Kumar, V.; Aktas, O.; Lee, J. W.; Adesida, I.
A fully monolithic AlGaN/GaN HEMT-based low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of -7.5 dB, input return loss of -7.5 dB, and output return loss of -15 dB at 8.5 GHz. The dc characteristics of individual 0.25-μm × 150-μm transistors were: maximum current density of 1.0 A/mm, maximum transconductance of 170 mS/mm and a threshold voltage of -6.8 V. The devices have a typical short circuit current gain cutoff frequency of 24.5 GHz and a maximum oscillating frequency of 48 GHz. The devices demonstrated a minimum noise figure of 1.6 dB with an associated gain of 10.6 dB at 10 GHz.
Open Access
Band alignment issues in metal/dielectric stacks: a combined photoemission and inverse photoemission study of the HfO 2/Pt and HfO 2/Hf systems
(Electrochemical Society, 2004) Sayan, S.; Bartynski, R.A.; Robertson J.; Suehle, J. S.; Vogel, E.; Nguyen, N. V.; Ehrstein, J.; Kopanski, J. J.; Süzer, Şefik; Holl, M. B.; Garfunkel, E.
We have studied the HfO 2/Hf and HfO 2/Pt systems by photoemission and inverse photoemission spectroscopies. It is found that the "effective workfunction" of metals in multilayer structures are different than their vacuum workfunctions and are modified by their interface dipoles at the metal/high-k interface. The effective workfunction of Hf is 4.4 eV whereas that of Pt is 5.3 eV, within the range of acceptable values for PMOS and NMOS respectively.
Open Access
Current transport mechanisms in plasma-enhanced atomic layer deposited AlN thin films
(A I P Publishing LLC, 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi
Here, we report on the current transport mechanisms in AlN thin films deposited at a low temperature (i.e., 200°C) on p-type Si substrates by plasma-enhanced atomic layer deposition. Structural characterization of the deposited AlN was carried out using grazing-incidence X-ray diffraction, revealing polycrystalline films with a wurtzite (hexagonal) structure. Al/AlN/ p-Si metal-insulator-semiconductor (MIS) capacitor structures were fabricated and investigated under negative bias by performing current-voltage measurements. As a function of the applied electric field, different types of current transport mechanisms were observed; i.e., ohmic conduction (15.2-21.5 MV/m), Schottky emission (23.6-39.5 MV/m), Frenkel-Poole emission (63.8-211.8 MV/m), trap-assisted tunneling (226-280 MV/m), and Fowler-Nordheim tunneling (290-447 MV/m). Electrical properties of the insulating AlN layer and the fabricated Al/AlN/p-Si MIS capacitor structure such as dielectric constant, flat-band voltage, effective charge density, and threshold voltage were also determined from the capacitance-voltage measurements.
Open Access
Design, fabrication, and characterization of normally-off GaN HEMTS
(2019-07) Gülseren, Melisa Ekin
GaN-based high-electron-mobility transistors (HEMTs) have been developing rapidly from the time when they were first demonstrated in the 1990s. They have consistently been presented as a displacement technology to silicon based power devices owing to the superior material properties of GaN such as high-electric breakdown field, high-electron saturation velocity, and high mobility. Normally-off GaN HEMT devices are particularly significant in power electronics applications. In this thesis, a comprehensive study of normally-off high-electron-mobility transistors is presented, including theoretical background review, theoretical analysis, physically-based device simulations, device fabrication and optimization and electrical characterization. p-GaN gate InAlN/GaN HEMT and recessed AlGaN/GaN MISHEMT devices have been successfully demonstrated.
Open Access
Effect of film thickness on the electrical properties of AlN films prepared by plasma-enhanced atomic layer deposition
(Institute of Electrical and Electronics Engineers Inc., 2015) Altuntas, H.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi
In this paper, AlN thin films with two different thicknesses, i.e., 7 and 47 nm, were deposited at 200 °C on p-type Si substrates by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia. To investigate the electrical characteristics of these AlN films, MIS capacitor structures were fabricated and characterized using current-voltage and high-frequency (1 MHz) capacitance-voltage measurements. The results showed that the current transport mechanism under accumulation mode is strongly dependent on the applied electric field and thickness of the AlN film. Possible conduction mechanisms were analyzed, and the basic electrical parameters were extracted and compared for AlN thin films with different thicknesses. Compared with 7-nm-thick film, a 47-nm-thick AlN film showed a lower effective charge density and threshold voltage along with a higher dielectric constant.
Open Access
Enhanced tunability of V-shaped plasmonic structures using ionic liquid gating and graphene
(Elsevier Ltd, 2016) Ozdemir, O.; Aygar, A. M.; Balci, O.; Kocabas, C.; Caglayan, H.; Özbay, Ekmel
Graphene is a strong candidate for active optoelectronic devices because of its electrostatically tunable optical response. Current substrate back-gating methods are unable to sustain high fields through graphene unless a high gate voltage is applied. In order to solve this problem, ionic liquid gating is used which allows substrate front side gating, thus eliminating the major loss factors such as a dielectric layer and a thick substrate layer. On the other hand, due to its two dimensional nature, graphene interacts weakly with light and this interaction limits its efficiency in optoelectronic devices. However, V-shaped plasmonic antennas can be used to enhance the incident electric field intensity and confine the electric field near graphene thus allowing further interaction with graphene. Combining V-shaped nanoantennas with the tunable response of graphene, the operation wavelength of the devices that utilize V-shaped antennas can be tuned in situ. In the present paper, we demonstrate a graphene-based device with ionic liquid gating and V- shaped plasmonic antennas to both enhance and more effectively tune the total optical response. We are able to tune the transmission response of the device for up to 389 nm by changing the gate voltage by 3.8 V in the mid-infrared regime.
Open Access
Low power Zinc-Oxide based charge trapping memory with embedded silicon nanoparticles
(ECS, 2014) Nayfeh, A.; Okyay, Ali Kemal; El-Atab, N.; Özcan, Ayşe; Alkış, Sabri
In this work, a bottom-gate charge trapping memory device with Zinc-Oxide (ZnO) channel and 2-nm Si nanoparticles (Si-NPs) embedded in ZnO charge trapping layer is demonstrated. The active layers of the memory device are deposited by atomic layer deposition (ALD) and the Si-NPs are deposited by spin coating. The Si-NPs memory exhibits a threshold voltage (Vt) shift of 6.3 V at an operating voltage of -10/10 V while 2.6 V Vt shift is obtained without nanoparticles confirming that the Si-NPs act as energy states within the bandgap of the ZnO layer. In addition, a 3.4 V Vt is achieved at a very low operating voltage of -1 V/1 V due to the charging of the Si-NPs through Poole-Frenkel emission mechanism at an electric field across the tunnel oxide E > 0.36 MV/cm. The results highlight a promising technology for future ultra-low power memory devices.
Open Access
Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure
(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.
A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Memristive behavior in a junctionless flash memory cell
(American Institute of Physics Inc., 2015) Orak, I.; Ürel, M.; Bakan, G.; Dana, A.
We report charge storage based memristive operation of a junctionless thin film flash memory cell when it is operated as a two terminal device by grounding the gate. Unlike memristors based on nanoionics, the presented device mode, which we refer to as the flashristor mode, potentially allows greater control over the memristive properties, allowing rational design. The mode is demonstrated using a depletion type n-channel ZnO transistor grown by atomic layer deposition (ALD), with HfO2 as the tunnel dielectric, AI2O3 as the control dielectric, and non-stoichiometric silicon nitride as the charge storage layer. The device exhibits the pinched hysteresis of a memristor and in the unoptimized device, R off/R on ratios of about 3 are presented with low operating voltages below 5 V. A simplified model predicts Roff/Ron ratios can be improved significantly by adjusting the native threshold voltage of the devices. The repeatability of the resistive switching is excellent and devices exhibit 106 s retention time, which can, in principle, be improved by engineering the gate stack and storage layer properties. The flashristor mode can find use in analog information processing applications, such as neuromorphic computing, where well-behaving and highly repeatable memristive properties are desirable.