A 1.2-V 4.2- <tex> $\hbox{ppm}/^{\circ}\hbox{C}$</tex> High-Order Curvature-Compensated CMOS Bandgap Reference

Duan, Quanzhen,Roh, Jeongjin IEEE 2015 IEEE Transactions on Circuits and Systems I: Regul Vol.62 No.3

<P>This study presents a high-precision CMOS bandgap reference (BGR) circuit with low supply voltage. The proposed BGR circuit consists of two BGR cores and a curvature correction circuit, which includes a current mirror and a summing circuit. Two BGR cores adopt conventional structures with the curvature-down characteristics. A current-mirror circuit is proposed to implement one of the BGR cores to have the curvature-up characteristic. Selection of the appropriate resistances in the BGR cores results in one reference voltage with a well balanced curvature-down characteristic and another reference voltage with an evenly balanced curvature-up characteristic. The summation of these reference voltages is proposed to achieve a high-order curvature compensation. This curvature correction circuit causes the proposed BGR circuit without any trimming to show a measured temperature coefficient (TC) as low as 4.2 <TEX>$\hbox{ppm}/^{\circ}\hbox{C}$</TEX> over a wide temperature range of 160 <TEX>$^{\circ}\hbox{C}$</TEX> <TEX>$(-\hbox{40}\sim \hbox{120}~^{\circ}\hbox{C})$</TEX> at a power supply voltage of 1.2 V. The average TC for 8 random samples is approximately 9.3 <TEX>$\hbox{ppm}/^{\circ}\hbox{C}$</TEX> . The measured power-supply rejection ratio (PSRR) of <TEX>$-$</TEX>30 dB is achieved at the frequency of 100 kHz. The total chip size is 0.063 <TEX>${\rm mm}^{2}$</TEX> with a standard 0.13-<TEX>$\mu{\rm m}$</TEX> CMOS process.</P>

A Delta–Sigma Modulator for Low-Power Analog Front Ends in Biomedical Instrumentation

Younghyun Yoon,Quanzhen Duan,Jaejin Yeo,Jeongjin Roh,Jongjin Kim,Dongwook Kim Institute of Electrical and Electronics Engineers 2016 IEEE transactions on instrumentation and measureme Vol.65 No.7

<P>This paper presents a high-resolution dual-integrating delta-sigma modulator (DI-DSM) for low-power analog front-end (AFE) circuits in biomedical instrumentation. The AFE contains a preamplifier and a switched-capacitor DS analog-to-digital converter. The proposed DI-DSM adopts two kinds of clock frequencies: one is the same as the conventional frequency and the other is one-half of the conventional frequency, which provides sufficient settling time for critical blocks. The proposed structure reduces harmonic distortions at the output of the preamplifier, since the preamplifier is given sufficient time to charge the sampling capacitor in the DSM. The use of a lower switching frequency at the critical blocks results in a significant reduction in the power consumption of both the preamplifier and the modulator. The proposed AFE chip is fabricated in a 65-nm CMOS process. The measurement results of the modulator show a peak signal-to-noise ratio (SNR) of 81.4 dB and a peak signal-to-noise-plus-distortion ratio (SNDR) of 80.4 dB, with a power consumption of 24.8 mu W at a supply voltage of 1 V and a signal bandwidth of 10 kHz. The complete AFE chip [which includes a preamplifier, a DI-DSM, a low-dropout (LDO) regulator, and a bandgap reference circuit (BGR)] shows a measured peak SNR of 79.3 dB and a measured peak SNDR of 77.0 dB with a preamplifier power of only 46.8 mu W (and 22.3 mu W for LDO, and 36.3 mu W for BGR).</P>

A single-electrode capacitive sensor using incremental delta–sigma architecture

Jung, Youngjae,Duan, Quanzhen,Roh, Jeongjin Springer-Verlag 2013 Analog integrated circuits and signal processing Vol.76 No.2

A 0.03 mm2 delta-sigma modulator with cascaded-inverter amplifier

Wang, Zhidong,Duan, Quanzhen,Roh, Jeongjin Springer-Verlag 2014 Analog Integrated Circuits and Signal Processing Vol.81 No.2

Palladium Nanostructures on GaN (0001): Evolution of Pd Hillocks, Voids, Nanoclusters and Nanoholes via Systematic Control of Annealing Temperature at Various Pd Thickness

Kunwar, Sundar,Sui, Mao,Zhang, Quanzhen,Pandey, Puran,Li, Ming-Yu,Lee, Jihoon American Scientific Publishers 2018 Journal of nanoelectronics and optoelectronics Vol.13 No.6

<P>Controllable synthesis of metallic nanostructures is of great importance in electronic, optical, catalytic, sensing and medical applications, in which the various corresponding properties can be directly tuned by the control of configuration, dimension and density of nanostructures. Here, the fabrication of self-assembled Pd nanostructures and porous GaN (0001) is demonstrated by the systematic control of annealing temperature and thickness of Pd thin films. The evolution of various Pd nanostructures is systematically presented and discussed in correlation with the diffusion of Pd adatoms, void nucleation and growth, Volmer-Weber growth model and surface and interface energy minimization mechanism. Depending on the systematic temperature control, the Pd nanostructures exhibit three distinctive growth regimes: tiny pits and hillocks along with void nucleation and growth (regime-I) between 400 and 600 degrees C, expanded void to the isolated nanoclusters (regime-II) between 650 to 750 degrees C and finally Pd nanoclusters assisted nanohole (NH) formation along with a GaN decomposition (regime-III) between 800 and 850 degrees C. Under an identical growth condition, the growth regimes shift along with the variation of Pd thickness due to the alteration in the required diffusion energy: that is the dewetting process occurs at relatively lower temperature for thinner initial Pd film and vice-versa. In addition, the evolution of the Pd nanostructures on GaN (0001) is closely associated with the optical characteristics such that photoluminescence (PL) and Raman intensity is high for low surface coverage whereas the average optical reflectance holds the reverse relationship.</P>

Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) Along With the Concurrent Influence of Diffusion, Ostwald's Ripening, and Sublimation

Pandey, Puran,Kunwar, Sundar,Sui, Mao,Zhang, Quanzhen,Li, Ming-Yu,Lee, Jihoon IEEE 2017 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. No.

<P>Silver nanoparticles (Ag NPs) have found a number of applications in various fields such as optoelectronics, sensors, and catalysts, and the optical, physical, and chemical properties of Ag NPs can be modified by the control of size, density, and configuration as well as their spacing. Therefore, in this paper, we demonstrate the size, shape, and spacing control of Ag NPs by the systematic control of annealing duration between 0 and 3600 s on sapphire (0001) (Al2O3). The Ag NPs show a sharp distinction in morphology along with the controlled duration at 20 and 14 nm thickness, and the evolution trend is systematically discussed based on the concurrent influence of surface diffusion, Ostwald's ripening, and sublimation. With the relatively thicker film of 20 nm, the fabrication of irregular and round NPs is demonstrated along with the gradually reduced size up on the annealing at 750 degrees C for the duration between 0 and 900 s. Between 1800 and 3600 s, tiny grain-like particles result as a consequence of an extensive sublimation. Meanwhile, with the film thickness of 14 nm at 400 degrees C, densely packed small NPs are resulted between 0 and 3600 s due to the limited surface diffusion. At the same time, the optical characterizations such as Raman and reflectance spectroscopy show a distinctive trend of spectra, i.e., intensity, peak position, and FWHM, based on the evolution of Ag NPs and are discussed in conjunction with the specific morphology and surface coverage of the Ag NPs.</P>

Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films

Kunwar, Sundar,Sui, Mao,Zhang, Quanzhen,Pandey, Puran,Li, Ming-Yu,Lee, Jihoon Springer Berlin Heidelberg 2017 Nano-micro letters Vol.9 No.2

<P>Silver (Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices. The target application and the performance can be inherently tuned by control of configuration, shape, and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire (0001) by controlling the Ag deposition thickness at different annealing environments in a plasma ion coater. In particular, the evolution of Ag particles (between 2 and 20 nm), irregular nanoclusters (between 30 and 60 nm), and nanocluster networks (between 80 and 200 nm) are found be depended on the thickness of Ag thin film. The results were systematically analyzed and explained based on the solid-state dewetting, surface diffusion, Volmer–Weber growth model, coalescence, and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature (750 °C) due to the sublimation and temperature-dependent characteristic of dewetting process. In addition, Raman and reflectance spectra analyses reveal that optical properties of Ag nanostructures depend on their morphology.</P><P/><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1007/s40820-016-0120-6) contains supplementary material, which is available to authorized users.</P>

Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting

Kunwar, Sundar,Pandey, Puran,Sui, Mao,Zhang, Quanzhen,Li, Ming-Yu,Lee, Jihoon SPRINGER SCIENCE + BUSINESS MEDIA 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1

<P>Si-based optoelectronic devices embedded with metallic nanoparticles (NPs) have demonstrated the NP shape, size, spacing, and crystallinity dependent on light absorption and emission induced by the localized surface plasmon resonance. In this work, we demonstrate various sizes and configurations of palladium (Pd) nanostructures on Si (111) by the systematic thermal annealing with the variation of Pd thickness and annealing temperature. The evolution of Pd nanostructures are systematically controlled by the dewetting of thin film by means of the surface diffusion in conjunction with the surface and interface energy minimization and Volmer-Weber growth model. Depending on the control of deposition amount ranging between 0.5 and 100 nm at various annealing temperatures, four distinctive regimes of Pd nanostructures are demonstrated: (i) small pits and grain formation, (ii) nucleation and growth of NPs, (iii) lateral evolution of NPs, and (iv) merged nanostructures. In addition, by the control of annealing between 300 and 800 °C, the Pd nanostructures show the evolution of small pits and grains, isolated NPs, and finally, Pd NP-assisted nanohole formation along with the Si decomposition and Pd-Si inter-diffusion. The Raman analysis showed the discrepancies on phonon modes of Si (111) such that the decreased peak intensity with left shift after the fabrication of Pd nanostructures. Furthermore, the UV-VIS-NIR reflectance spectra revealed the existence of surface morphology dependent on absorption, scattering, and reflectance properties.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-017-2138-1) contains supplementary material, which is available to authorized users.</P>

Fabrication and determination of growth regimes of various Pd NPs based on the control of deposition amount and temperature on <i>c</i>-plane GaN

Sui, Mao,Kunwar, Sundar,Pandey, Puran,Zhang, Quanzhen,Li, Ming-Yu,Lee, Jihoon Published for the Materials Research Society by th 2017 Journal of materials research Vol.32 No.18

<▼1><B>Abstract</B><P/></▼1><▼2><P>Palladium (Pd) nanostructures have been actively adapted for various applications and their properties and applicability closely depend on their shape, size, and density. In this paper, the evolution of self-assembled Pd nanostructures on the hexagonal <I>c</I>-plane GaN is presented by the systematical control of Pd deposition amount (DA) at distinctive temperatures. Pd nanostructures of various configurations, sizes, and densities are demonstrated based on the solid-state dewetting of Pd thin films and a clear distinction in the growth regimes is observed. Three growth regimes are clearly observed depending on the variation of DA, i.e., (i) the agglomeration of Pd nanoparticles, (ii) the coalescence of wiggly Pd nanostructures, and finally (iii) the growth of nanovoids and layers. Owing to the temperature-dependent dewetting process, the growth regimes are markedly shifted, resulting in the distinctive Pd nanostructures within the identical DA range. The results are discussed in conjunction with the surface diffusion, Volmer-Weber and coalescence growth model, and surface/interface energy minimization mechanism. In addition, the evolution of optical properties, emission band, and lattice properties are probed by reflectance, photoluminescence, and Raman spectroscopy, which exhibit varying spectral intensity and peak positions according to the surface morphology of Pd nanostructures.</P></▼2>

Morphological, Structural and Optical Evolution of Ag Nanostructures on c-Plane GaN Through the Variation of Deposition Amount and Temperature

Mao Sui,Ming‑Yu Li,Puran Pandey,Quanzhen Zhang,Sundar Kunwar,Jihoon Lee 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.2

Owing to their tunable properties, Ag nanostructures have been widely adapted in various applications and the morphologicalcontrol can determine their performance and effectiveness. In this work, we demonstrate the morphological and opticalevolution of Ag nanostructures on GaN (0001) by the systematic control of deposition amount at two distinctive annealingtemperatures. Based on the Volmer–Weber and coalescence growth models, the nanostructure growth commenced by thethermal solid-state-dewetting evolve in terms of size, density and configuration. At 450 °C, the round-dome shaped Agnanoparticles (regime I), irregular Ag nano-mounds (regime II) and void-layer structures (regime III) are observed alongwith the gradually increased deposition amount. As a sharp distinction, the solid state dewetting process occur more radicallyat 700 °C and also, the Ag sublimation and the effect on the nanostructure formation are observed in a clear regime shiftscaled by the deposition amount. Meanwhile, a strong dependency of reflectance spectra evolution on the Ag nanostructuremorphology is witnessed for both sets. In particular, Ag dipolar resonance peaks are significantly red-shifted from VIS toNIR regions along with the nanostructure evolution. The reflectance, PL and Raman intensity variation are also observedand discussed based on the evolution of Ag nanostructures.