AlN/GaN-based MOS-HEMT technology: processing and device results

Process development of AlN/GaN MOS-HEMTs is presented, along with issues and problems concerning the fabrication processes. The developed technology uses thermally grown Al<sub>2</sub>O<sub>3</sub> as a gate dielectric and surface passivation for devices. Significant improvement in device performance was observed using the following techniques: (1) Ohmic contact optimisation using Al wet etch prior to Ohmic metal deposition and (2) mesa sidewall passivation. DC and RF performance of the fabricated devices will be presented and discussed in this paper

AlN/GaN MOS-HEMTs technology

The ever increasing demand for higher power devices at higher frequencies has prompted much research recently into the aluminium nitride/gallium nitride high electron mobility transistors (AlN/GaN HEMTs) in response to theoretical predictions of higher performance devices. Despite having superior material properties such as higher two-dimensional electron gas (2DEG) densities and larger breakdown field as compared to the conventional aluminium gallium nitride (AlGaN)/GaN HEMTs, the AlN/GaN devices suffer from surface sensitivity, high leakage currents and high Ohmic contact resistances. Having very thin AlN barrier layer of ∼ 3 nm makes the epilayers very sensitive to liquids coming in contact with the surface. Exposure to any chemical solutions during device processing degrades the surface properties, resulting in poor device performance. To overcome the problems, a protective layer is employed during fabrication of AlN/GaN-based devices. However, in the presence of the protective/passivation layers, formation of low Ohmic resistance source and drain contact becomes even more difficult. In this work, thermally grown aluminium oxide (Al2O3) was used as a gate di- electric and surface passivation for AlN/GaN metal-oxide-semiconductor (MOS)-HEMTs. Most importantly, the Al2O3 acts as a protection layer during device processing. The developed technique allows for a simple and effective wet etching optimisation using 16H3PO4:HNO3:2H2O solution to remove Al from the Ohmic contact regions prior to the formation of Al2O3 and Ohmic metallisation. Low Ohmic contact resistance (0.76Ω.mm) as well as low sheet resistance (318Ω/square) were obtained after optimisation. Significant reduction in the gate leakage currents was observed when employing an additional layer of thermally grown Al2O3 on the mesa sidewalls, particularly in the region where the gate metallisation overlaps with the exposed channel edge. A high peak current ∼1.5 A/mm at VGS=+3 V and a current-gain cutoff frequency, fT , and maximum oscillation frequency, fMAX , of 50 GHz and 40 GHz, respectively, were obtained for a device with 0.2 μm gate length and 100 μm gate width. The measured breakdown voltage, VBR, of a two-finger MOS-HEMT with 0.5μm gate length and 100 μm gate width was 58 V. Additionally, an approach based on an accurate estimate of all the small-signal equivalent circuit elements followed by optimisation of these to get the actual element values was also developed for AlN/GaN MOS-HEMTs. The extracted element values provide feedback for further device process optimisation. The achieved results indicate the suitability of thermally grown Al2O3 for AlN/GaN-based MOS-HEMT technology for future high frequency power applications

Surface Roughness and Grain Size Characterization of Annealing Temperature Effect for Growth Gallium and Tantalum Doped Ba0.5 Sr0.5TiO3Thin Film

Thin films 10 % gallium oxide doped barium strontium titanate (BGST) and 10 % tantalum oxide doped barium strontium titanate (BTST) were prepared on p-type Si (100) substrates using chemical solution deposition (CSD) method with 1.00 M precursor. The films were deposited by spin coating method with spinning speed at 3000 rpm for 30 seconds. The post deposition annealing of the films were carried out in a furnace at 200oC, 240oC, 280oC (low temperature) for 1 hour in oxygen gas atmosphere. The surface roughness and grain size analysis of the grown thin films are described by atomic force microscope (AFM) method at 5000 nm x 5000 nm area. The rms surface roughness BGST thin films at 5000 nm x 5000 nm area are 0.632 nm, 0.564 nm, 0.487 nm for temperature 200oC, 240oC, 280oC, respectively, whereas the grain size (mean diameter) are 238.4 nm, 219.0 nm, 185.1 nm for temperature 200oC, 240oC, 280oC, respectively. In fact, to increase annealing temperature from 200oC to 280oC would result in decreasing the rms roughness and grain size. Therefore, rms roughness and grain size would have the strong correlation annealing temperature. Received: 9 November 2008; Revised: 24 August 2009; Accepted: 25 August 200

The troubling concept of class: reflecting on our ‘failure’ to encourage sociology students to re-cognise their classed locations using autobiographical methods

The troubling concept of class: reflecting on our ‘failure’ to encourage sociology students to re-cognise their classed locations using autobiographical methods Abstract This paper provides a narrative of the four authors‟ commitment to auto/biographical methods as teachers and researchers in „new‟ universities. As they went about their work, they observed that, whereas students engage with the gendered, sexualised and racialised processes when negotiating their identities, they are reluctant or unable to conceptualise „class-ifying‟ processes as key determinants of their life chances. This general inability puzzled the authors, given the students‟ predominantly working-class backgrounds. Through application of their own stories, the authors explore the sociological significance of this pedagogical „failure‟ to account for the troubling concept of class not only in the classroom but also in contemporary society

PEMANFAATAN SISTEM PENAMPUNGAN DAN PERPIPAAN AIR BERBASIS TENAGA SURYA UNTUK MENGATASI KEKERINGAN DAN MENINGKATKAN HASIL PERTANIAN KELOMPOK TANI MEKAR JAYA

Program pengabdian masyarakat ini bertujuan untuk membantu Kelompok Tani Mekar Jaya dalam mengatasi permasalahan kekeringan yang sering terjadi, terutama pada musim kemarau, yang berdampak signifikan terhadap produktivitas pertanian. Melalui sistem penampungan air dan perpipaan berbasis tenaga surya, para petani dapat memperoleh akses air yang lebih stabil dan berkelanjutan tanpa bergantung sepenuhnya pada energi konvensional. PKM ini meliputi beberapa tahapan utama, sosialisasi, pelatihan yang mulai dari perencanaan desain sistem, pemasangan panel surya, pipa air, hingga pelatihan penggunaan dan perawatan teknologi kepada anggota kelompok tani, pendampingan instalasi secara langsung, evaluasi dan keberlanjuutan. Dengan memanfaatkan energi surya yang melimpah di daerah tersebut, sistem ini menyediakan solusi ramah lingkungan yang mampu memenuhi kebutuhan air untuk irigasi lahan pertanian secara efisien. Hasil dari implementasi sistem ini menunjukkan adanya peningkatan produksi pertanian yang signifikan serta berkurangnya ketergantungan petani terhadap pasokan air dari sumber lain atau yang menggunakan pompa diesel yang tentu saja berdampak pada kurangnya biaya produksi/ pertanian. Selain itu, program ini juga berhasil meningkatkan keterampilan teknis para petani dalam memelihara dan mengoperasikan teknologi pompanisasi berbasis energi terbarukan dengan nilai hasil observasi >80 (kategori sangat baik). selain itu dihasilkan sistem penampungan air dengan perpipaan tetes (kapasitas >17.000 liter). Melalui PKM ini, diharapkan keberlanjutan pertanian dapat lebih terjamin serta menjadi contoh bagi daerah lain yang menghadapi tantangan serupa

The Effect of Different Dielectric Materials in Designing High-Performance Metal-Insulator-Metal (MIM) Capacitors

A Metal-Insulator-Metal (MIM) capacitor with high capacitance, high breakdown voltage, and low leakage current is aspired so that the device can be applied in many electronic applications. The most significant factors that affect the MIM capacitor’s performance is the design and the dielectric materials used. In this study, MIM capacitors are simulated using different dielectric materials and different number of dielectric layers from two layers up to seven layers.  The effect of the different dielectric constants (k) to the performance of the MIM capacitors is also studied, whereas this work investigates the effect of using low-k and high-k dielectric materials. The dielectric materials used in this study with high-k are Al2O3 and HfO2, while the low-k dielectric materials are SiO2 and Si3N4. The results demonstrate that the dielectric materials with high-k produce the highest capacitance. Results also show that metal-Al2O3 interfaces increase the performance of the MIM capacitors. By increasing the number of dielectric layers to seven stacks, the capacitance and breakdown voltage reach its highest value at 0.39 nF and 240 V, respectively

Design of on-chip temperature-based digital signal processing for customized wireless microcontroller

Dramatic rises in power density and die sizes inside system-on-chip (SoC) design have led to the thermal issue. High temperatures or uneven temperature distributions may result not only in reliability issues, also has become the biggest issue that can limit the system performance.  This paper presents the design and simulation of a temperature-based digital signal processing unit for modern system-on-chip design using the Verilog HDL. This design provides continuous monitoring of temperature and reacts to specified conditions. The simulation of the system has been done on Synopsys Software. The result showed that temperature monitoring process is within the temperature range due to the incorporation of an interrupt-based system and with an advantage of minimum chip area required

Self-switching diodes as RF rectifiers: evaluation methods and current progress

In the advancement of the Internet of Things (IoT) applications, widespread uses and applications of devices require higher frequency connectivity to be explored and exploited. Furthermore, the size, weight, power and cost demands for the IoT ecosystems also creates a new paradigm for the hardware where improved power efficiency and efficient wireless transmission needed to be investigated and made feasible. As such, functional microwave detectors to detect and rectify the signals transmitted in higher frequency regions are crucial. This paper reviewed the practicability of self switching diodes as Radio Frequency (RF) rectifiers. The existing methods used in the evaluation of the rectification performance and cut-off frequency are reviewed, and current achievements are then concluded. The works reviewed in this paper highlights the functionality of SSD as a RF rectifier with design simplicity, which may offer cheaper alternatives in current high frequency rectifying devices for application in low-power devices