Browsing by Author "Liu, Po-Chun"

Now showing 1 - 13 of 13

A 1.69 Gb/s Area-Efficient AES Crypto Core with Compact On-the-fly Key Expansion Unit
(2009)
Liu, Po-Chun
;
Chang, Hsie-Chia
;
Lee, Chen-Yi
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The AES algorithm published in 2001 is now the most popular symmetric encryption algorithm. Several implementations have beed proposed but few of them considered the hardware cost and the throughput as a whole. This paper presents an AES core to be capable of both encryption and decryption with three different key lengths: 128-, 192-, and 256-bit. The overall hardware cost was optimized by a very compact on-the-fly key expansion unit and a highly integrated encryption/decryption datapath. The compact on-the-fly key expansion unit is achieved by sharing expansion processes of different key lengths. The integrated data datapath shares hardware resources between encryption and decryption. After manufactured in 90nm CMOS technology, the area of the chip is 15,577 equivalent gates with throughput up to 1.69 Gb/s operating at 131.8 MHz.
A Dual-Field Elliptic Curve Cryptographic Processor with a Radix-4 Unified Division Unit
(2011)
Chen, Yao-Lin
;
Lee, Jen-Wei
;
Liu, Po-Chun
;
Chang, Hsie-Chia
;
Lee, Chen-Yi
To enhance the data security in network communications, this paper presents a dual-field elliptic curve cryptographic processor (DECP) supporting all finite field operations and elliptic curve (EC) functions. Based on the fast radix-4 unified division algorithm, the execution time can be significantly reduced by a factor of three. By exploiting the hardware sharing and the ladder selection techniques, the proposed 160-bit and 256-bit DECP can have competitive execution cycle with only 0.29mm(2) and 0.45mm(2) silicon area in 90nm CMOS technology. In addition, the operating frequency in dual field can be increased by applying the data-path separation method and the degree checker. Our proposed DECP is over 2 similar to 6 times better in area-time product than relative works.
A Low Overhead DPA Countermeasure Circuit Based on Ring Oscillators
(2010-07-01)
Liu, Po-Chun
;
Chang, Hsie-Chia
;
Lee, Chen-Yi
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Side-channel attacks, particularly differential power analysis (DPA) attacks, are efficient ways to extract secret keys of the attacked devices by leaked physical information. To resist DPA attacks, hiding and masking methods are commonly used, but it usually resulted in high area overhead and performance degradation. In this brief, a DPA countermeasure circuit based on digital controlled ring oscillators is presented to efficiently resist the first-order DPA attack. The implementation of the critical S-box of the advanced encryption standard (AES) algorithm shows that the area overhead of a single S-box is about 19% without any extra delay in the critical path. Moreover, the countermeasure circuit can be mounted onto different S-box implementations based on composite field or look-up table (LUT). Based on our approach, a DPA-resistant AES chip can be proposed to maintain the same throughput with less than 2K extra gates.
A True Random-Based Differential Power Analysis Countermeasure Circuit for an AES Engine
(2012-02-01)
Liu, Po-Chun
;
Chang, Hsie-Chia
;
Lee, Chen-Yi
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The differential power analysis (DPA) has become a big threat to crypto chips since it can efficiently disclose the secret key without much effort. Several methods have been proposed in literatures to resist the DPA attack, but they largely increase the hardware cost and severely degrade the throughput. In this brief, a security problem based on ring oscillators is resolved by a new architecture with self-generated true random sequence. The true random-based architecture is implemented with an Advanced Encryption Standard (AES) crypto engine using UMC 90-nm CMOS technology. The DPA-resistant AES engine can achieve 2.97-Gb/s throughput at an operating frequency of 255 MHz with a 0.104-mm(2) cell area. The proposed DPA countermeasure circuit has only 6.2% area and 18.5% power overhead without throughput degradation.
Characteristics of a-Plane Green Light-Emitting Diode Grown on r-Plane Sapphire
(2009-08-15)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
In this work, we have successfully grown a-plane green light-emitting diodes (LEDs) on r-plane sapphire and investigated the device characteristics of a-plane green LEDs. The apparent emission polarization anisotropy was observed and the polarization degree was as high as 67.4%. In addition, the electroluminescence (EL) spectra first revealed a wavelength blue-shift with increasing drive current to 20 mA, which could be attributed to the band-filling effect, and then the EL peak become constant. The current-voltage curve showed the forward voltage of a-plane LED grown on r-plane sapphire substrate was 3.43 V and the differential series resistance was measured to be about 24 Omega as 20-mA injected current. Furthermore, the output power was 240 mu W at 100-mA drive current.
Comparison between extended microtunnels along different crystal orientations in GaN
(2008)
Wu, Pei-Lun
;
Huang, Hsin-Hsiung
;
Zeng, Hung-Yu
;
Liu, Po-Chun
;
Lai, Chih-Ming
Triangular prism-like extended microtunnels (EMTs) can be easily formed in specially designed cpitaxial lateral overgrowth GaN thick films by selective wet chemical etching in molten potassium hydroxide (KOH), In this study, extended microtunnels along the < 1100 > and the < 1120 > directions were fabricated and compared. If tunnels along the < 1100 > direction, the (1122) planes would be the etch stop plane. While the tunnels along < 1120 > direction, the etch stop plane would become to (1011) planes. The activation energies of wet chemical etch for the {1122} planes and the (1011) planes were determined to be 23.6 kcal/mol (1.02 eV) and 22.8 kcal/mol (0.99 eV) using Arrhenius plot. On the other hand, the etching depths of the tunnels along the < 1100 > direction were more than twice the depths of the tunnels along the < 1120 > direction during the same etching time. The highest etch rate of the tunnels along the axial direction can reach 1000 mu m/hr in < 1100 > direction, which is believed to be the highest etch rate of GaN ever reported. Additional crystal facet of m-plane in GaN was also observed in the sample with extended microtunnels along the < 1120 > direction. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Crystal quality improvement of a-plane GaN using epitaxial lateral overgrowth on nanorods
(2010-04-01)
Ling, Shih-Chun
;
Chao, Chu-Li
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on nanorod GaN template. The scanning electron microscope images showed the fully coalesced regrowth process completed within only 2 mu m thickness. The a-plane GaN films grown on nano-rod template showed superior surface quality and less surface pits. The on-axis and off-axis FWHMs of X-ray rocking curves decreased with the increase in the etching depth of the nano-rod template. TEM analysis revealed that the dislocation density was reduced to around 1.2 x 10(9) cm(-2) by the nano-rod epitaxial lateral overgrowth. In addition, the photoluminescence intensity of the a-plane GaN was enhanced significantly. These results demonstrated the opportunity of achieving a-plane GaN films with high crystal quality via nano-rod epitaxial lateral overgrowth. (C) 2009 Elsevier B.V. All rights reserved.
Freestanding high quality GaN substrate by associated GaN nanorods self-separated hydride vapor-phase epitaxy
(2009-08-03)
Chao, C. L.
;
Chiu, C. H.
;
Lee, Y. J.
;
Kuo, H. C.
;
Liu, Po-Chun
This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide (SiO(2)) were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy (HVPE). The passivation of the sidewalls coated with SiO(2) prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.
High-Quality Free-standing GaN Thick-films Prepared by Hydride Vapor Phase Epitaxy using Stress Reducing Techniques
(2009)
Huang, Hsin-Hsiung
;
Lee, Wei-I
;
Chen, Kuei-Ming
;
Chu, Ting-Li
;
Wu, Pei-Lun
As one of the most mature techniques for manufacturing free-standing GaN substrates, hydride vapor phase epitaxy (HVPE) always encounters problems associated with residue thermal stress, such as GaN bending and cracking during and after growth. This work presents a patterning approach and a non-patterning approach to reduce stress in thick GaN films grown on sapphires by HVPE. The patterning approach, forming dot air-bridged structures, adopted standard photolithography to fabricate hexagonally aligned patterns of dots on GaN templates. Following HVPE growth, regular voids were formed and buried in the GaN thick-films. These voids helped to relax the stress in the GaN thick-films. In the non-patterning approach, thick GaN films were simply grown at a specially set sequence of ramping temperatures during HVPE growth without any patterned structure. This temperature-ramping technique, gives crack-free high-quality 2"-diameter GaN films, thicker than 250 mu m, on sapphires in high yields. These thick GaN films can be separated from sapphire using conventional laser-induced lift-off processes, which can be followed by subsequent HVPE regrowths. A 600 mu m-thick free-standing GaN films has a typical dislocation density of around 4x10(6) cm(-2) with a full width at half maximum (FWHM) in the high resolution X-ray diffraction (HRXRD) spectrum of GaN (002) of around 150 arcsec. The residual stress in the thick GaN films was analyzed by micro-Raman spectroscopy. The effectiveness of the patterning and the non-patterning techniques in reducing the strain in GaN films is discussed. The advantages and weaknesses of the patterning and the non-patterning techniques will be elucidated.
Nanorod epitaxial lateral overgrowth of a-plane GaN with low dislocation density
(2009-06-22)
Ling, Shih-Chun
;
Chao, Chu-Li
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template. The investigation of x-ray diffraction showed that the strain in a-plane GaN grown on r-plane sapphire could be mitigated. The average threading dislocation density estimated by transmission electron microscopy was reduced from 3x10(10) to 3.5x10(8) cm(-2). From the temperature-dependent photoluminescence, the quantum efficiency of the a-plane GaN was enhanced by the nanorod epitaxial lateral overgrowth (NRELOG). These results demonstrated the opportunity of achieving a-plane GaN films with low dislocation density and high crystal quality via NRELOG.
Performance Enhancement of a-Plane Light-Emitting Diodes Using InGaN/GaN Superlattices
(2009-04-01)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
We have fabricated a-plane light-emitting diodes (LEDs) with inserted InGaN/GaN superlattices. The structural characteristics and device performance of a-plane light-emitting diodes with/without superlattices were also identified. Transmission electron microscope (TEM) images revealed that the threading dislocation (TD) density for the sample using superlattices was reduced from 3 x 10(10) cm(-2) down to similar to 9 x 10(9) cm(-2). The electroluminescence (EL) intensity of the sample with InGaN/GaN superlattices was enhanced by a factor of 3.42 times to that of the conventional sample without InGaN/GaN superlattices. Furthermore, we observed that the polarization degree of a-plane LEDs with superlattices (56.3%) was much higher than that without superlattices (27.4%). A series of experiments demonstrated that the feasibility of using InGaN/GaN superlattices for the TD reduction and the improvement of luminescence performance in a-plane III-nitride devices. (C) 2009 The Japan Society of Applied Physics
Strain-reduced GaN thick-film grown by hydride vapor phase epitaxy utilizing dot air-bridged structure
(2009-05-01)
Huang, Hsin-Hsiung
;
Chao, Chu-Li
;
Chi, Tung-Wei
;
Chang, Yu-Lin
;
Liu, Po-Chun
A 300 pm GaN thick-film, in diameter 1.5 in, was demonstrated without any crack by hydride vapor phase epitaxy (HVPE) growth. The technique used in relaxing the residual stress caused by differences of thermal expansion coefficients (TEC) and lattice constants between GaN and sapphire substrate to prevent GaN film from crack is called a dot air-bridged structure. After the laser lift-off process, 300-mu m-thick freestanding GaN wafer, in diameter 1.5 in, could be fabricated. The compressive stress in the dot air-bridged structure was measured by micro-Raman spectroscopy with the E(2)(high) phonon mode. The compressive stress could be reduced to as small as 0.04 GPa, which could prevent the crack during the epitaxial process for GaN growth by HVPE. It is important to obtain a large-area crack-free GaN thick-film, which can be used for fabricating freestanding GaN wafer. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Triangular extended microtunnels in GaN prepared by selective crystallographic wet chemical etching
(2008)
Huang, Hsin-Hsiung
;
Wu, Pei-Lun
;
Zeng, Hung-Yu
;
Liu, Po-Chun
;
Chi, Tung-Wei
Extended microtunnels with triangular cross sections in thick GaN films were demonstrated using wet chemical etching on specially designed epitaxial lateral overgrowth structures. For tunnels along the < 1 (1) over bar 00 > and < 11 (2) over bar0 > directions of GaN, the {11 (22) over bar} and {10 (11) over bar} facets are the etch stop planes with activation energies of 23 kcal/mol determined by wet chemical etching. The axial etching rate of the tunnels in the < 1 (1) over bar 00 > direction is twice as large than that along the < 11 (2) over bar0 > direction. The highest etching rate of the tunnels in the axial direction is 1000 mu m/h. (C) 2008 The Electrochemical Society.