无铅焊接中Lift-off现象产生的原因及抑制对策

本文首次提出三要素法来解释Lift-off的形成机理。相比传统的“Bi-Segregation”失效机理,“三要素法”可以解释含Bi和不含Bi的所有无铅钎料产生或不产生Lift-off的原因,并由此找出了Lift-off的抑制对策。

低温砷化镓的外延lift-off和范德华贴附研究

研究了低温砷化镓的外延lift-off和基于范德华力在石英新衬底上贴附的实验方法：腐蚀掉100nm厚的AlAs牺牲层，将外延生长的500nm厚的低温砷化镓（LT-GaAs）从生长衬底上揭下（lift-off），借助于范德华力将LT-GaAs外延膜贴附在新衬底上。Lift—off之前在LT-GaAs表面上滴附黑蜡，以增强在lift-off过程中对LT-GaAs的保护，和加快反应气体扩散离开反应区的过程。针对500nm厚的LT-GaAs外延薄膜的揭起和贴附，给出了低温砷化镓的最佳lift-off尺寸和提高范德华力贴附质量的实验技术。此外还给出了利用所得到的lift-off后的LT-GaAs制备的共平面条形结构光导开关的时间特性：上升时间小于1．5ps，FWHM小于2ps。

Experimental analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry （PDA） in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the X^2-test for these probability distributions, that the probability density functions （pdf＇s） of the sand particles＇ lift-off and incident velocities as well as their vertical com- ponents are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions, These pdf＇s depend on not only the sand particle diameter but also the wind speed.

Sand particle lift-off velocity measurements and numerical simulation of mass flux distributions in a wind tunnel

Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probability distribution of lift-off velocity can be expressed as a lognormal function, while that of lift-off angle follows an exponential function. The probability distribution of lift-off angle conditioned for each lift-off velocity also follows an exponential function, with a slope that becomes steeper with increasing lift-off velocity. This implies that the probability distribution of lift-off velocity is strongly dependent on the lift-off angle. However, these lift-off parameters are generally treated as an independent joint probability distribution in the literature. Numerical simulations were carried out to investigate the effects of conditional versus independent joint probability distributions on the vertical sand mass flux distribution. The simulation results derived from the conditional joint probability distribution agree much better with experimental data than those from the independent ones. Thus, it is better to describe the lift-off velocity of saltating sand particles using the conditional joint probability distribution. These results improve our understanding of saltation processes in wind-blown sand.

Spatiotemporal evolution of high-aspect-ratio filamentary trace in sapphire of picosecond pulse burst-mode for laser lift-off

The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.

Epitaxial Lift-Off of Flexible GaN‑Based HEMT Arrays with Performances Optimization by the Piezotronic Effect

High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is required.Herein,a large-sized(>2 cm^(2))of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique.The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas(2DEG)and phonons.The saturation current of the flexible HEMT is enhanced by 3.15%under the 0.547%tensile condition,and the thermal degradation of the HEMT was also obviously suppressed under compressive straining.The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism.This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs,but also demonstrates a low-cost method to optimize its electronic and thermal properties.

国产Lift-Off光刻胶在空间用太阳电池中的应用

选用两种较为典型的国产Lift-Off光刻胶(A和B)进行了实验优化,并进行了电极蒸镀后的牢固度测试、电致发光测试和电性能测试。在牢固度测试中发现,A电池样品有掉栅现象,B电池样品没有出现掉栅现象。通过EL测试和电性能测试分析证明,A电池的电极与太阳电池基体存在局部的接触不良现象。通过实验筛选出了一种应用前景较好的B型号国产Lift-Off负性光刻胶,有望经过进一步验证和优化后逐步应用在空间用太阳电池生产中。

萘酚基酚醛树脂的合成及其在lift-off光刻胶中的应用

首先以α-萘酚、间甲酚、甲醛为单体,通过缩聚反应合成了萘酚基酚醛树脂NAPR,随后与二碳酸二叔丁酯(DBDC)反应制备了一系列t-BOC改性的萘酚基酚醛树脂NAPR-BOC。用红外(FT-IR)、核磁(1 H NMR)、凝胶色谱(GPC)、热失重分析(TGA)对其结构及性能进行了表征。以NAPR-BOC-2为基体树脂配制成lift-off光刻胶,测试了光刻胶的分辨率、形貌和耐热性,得到的光刻胶分辨率最大为0.6μm,耐热可达130℃。

Fabrication of THz Dipole Antenna Using Lift-off Method

The microfabrication technique for THz dipole antenna,"lift-off" was studied in this paper.Its procedure has been examined in detail,and discreetly tweaked.Particularly,Chlorobenzene is suggested to assist the formation of undercut indispensible for fulfilling "lift-off".The experimental results of fabricated antennas confirm the effectiveness of this method.

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water‑Etching and Transfer Process

Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering.In recent years,lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations.Moreover,twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures.A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process,which could provide some insight in to the physical phenomena.In this work,the La_(0.67)Sr_(0.33)MnO_(3)(001)/0.7Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.3PbTiO_(3)(011)(LSMO/PMN-PT)heterostructures with 45.and 0.twist angles were assembled via water-etching and transfer process.The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO<110>.A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO[110]easy axis is observed for the 45°Sample by applying a 7.2 kV cm^(−1)electrical field,significantly different from a uniaxial anisotropy with LSMO[100]easy axis for the 0°Sample.The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45°twist angle causes different lattice distortion of LSMO,thereby enhancing both the fourfold and uniaxial anisotropy.This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

喷射火灾脱火法施救的实验研究

鉴于目前常见的大、中型喷射火灾施救普遍存在效率低、代价高而且方法、器材的通用性差等问题,针对所提出的先脱后灭的脱火法灭火新思想,用专门制作的原理性实验装置对其进行实验分析。结果表明:随着流量的增大,扰流的脱火效能明显加强;随着入射角度的减小,脱火效能逐渐增大;入射距离对脱火效能的影响则存在"平稳区",该区域随着流量的增大而减小。

火焰周边扰流脱火效能的图像分析技术

脱火现象的分析研究是喷射火灾脱火法施救等诸多技术的重要基础。论文提出并较为深入地研究了火焰周边扰动气流脱火效能的图像分析技术。详细阐述了技术思想,分析了图像的获取及其信息的处理过程,建立了求解表征扰流脱火效能的火焰脱开距离数学模型,并通过专门设计的实验,初步验证了这一分析技术的可行性,为脱火现象的分析研究提供了重要的技术基础。

纳米多孔金薄膜及其微电极结构的制备

结合磁控溅射、lift-off工艺和脱合金法制备了纳米多孔金薄膜及其微电极结构。首先利用磁控溅射法和lift-off技术制备了金银合金叉指型微薄膜电极结构,然后采用浓硝酸通过脱合金方法进一步制备出纳米多孔金薄膜微电极结构。本文系统研究了腐蚀时间对磁控溅射金银合金薄膜去合金化所制备的纳米多孔金薄膜形貌、组分和结构的影响。利用X射线衍射、场发射扫描电子显微镜和透射电子显微镜表征了纳米多孔金薄膜微电极的结构和形貌。结果表明纳米多孔金主要呈现(111)晶面,且脱合金时间对纳米多孔结构形成与演化有明显的影响。随着腐蚀时间增加,纳米多孔金薄膜孔隙度增加,金韧带分布更加均匀,逐渐形成均匀的具有高表面积的开放式多孔结构。

入射角度对喷射火脱火效能的影响分析

为研究入射角度对脱火效能的影响规律,借助THORNTON模型和火焰倾角计算公式对其进行理论分析,并设计专门的实验装置具体研究双向人工扰流入射角度与脱火效能之间的关系。结果表明:在水平面和竖直面两个不同平面内,脱火效能均随着入射角度的改变呈现明显的变化,水平面两扰流夹角120°、竖直面入射对称角30°时的脱火效能最大。合理设置入射角度,有助于提高双向人工扰流的脱火效能。

多晶金刚石薄膜日盲紫外探测器件的电极制备

通过在直流等离子体喷射化学气相沉积(DC-PJCVD)法生长的多晶金刚石薄膜上制备Au叉指电极,构建了金属-半导体-金属(MSM)结构的日盲紫外探测器件。研究了不同光刻工艺对制备的金刚石探测器件性能的影响。结果表明,lift-off光刻工艺所制备的器件性能明显优于湿法光刻工艺器件,其I_(light)提高了4.4倍,光暗电流比提高了6.8倍,在25 V电压下响应度提高了9倍,达到了0.15 A/W。在此基础上通过lift-off光刻工艺制备了Au、Ti、Ti/Au和Ag四种不同金属的叉指电极,对比了不同金属电极制备的金刚石紫外探测器件的性能差异。其中Ag电极由于存在势垒隧穿效应引起的增益,在四种电极中性能表现最佳,在25 V偏压下其I_(light)高达0.21μA,响应度提升到0.78 A/W,性能与已有报道的器件性能相当。与普通Au电极制备的器件相比,其光电流提高了5.2倍,光暗电流比提升了7倍,响应度提高了5.2倍。

喷射火双向人工扰流脱火的可控参数试验研究

为解决喷射火单向人工扰流脱火方法效率低的问题,设计并制作喷射火双向人工扰流脱火方法试验装置,分析扰流流量、入射角度、入射高度和入射距离等4个主要可控参数对脱火距离的影响。结果表明:随着扰流流量的增加,脱火距离呈现先增大再减小的趋势;水平面扰流夹角逐渐增大时,脱火距离先增大再减小,竖直面入射夹角逐渐增大时,脱火距离逐渐减小;入射高度为-2～2 mm时脱火距离较大,超出此范围后脱火距离迅速减小;扰流流量不变时,随着入射距离的增大,脱火距离有逐渐增大的趋势。合理设定双向人工扰流的可控参数,有助于提高脱火效能。

星形电极介电泳芯片

提出了一种利用负介电泳力在介电泳芯片上富集聚苯乙烯(PS)微球的有效方法:采用lift-off工艺在玻璃衬底上设计并制作了星形结构的微电极,在高频交流信号作用下,星形电极芯片能够提供一个特定的非均匀电场,从而产生负介电泳力。研究了交流信号的幅值和频率、工作液电导率和浓度等参数对PS微球富集效果的影响。结果显示,在交流信号的电压参数VP-P为9 V,频率参数为1 MHz时,低电导率PS微球悬浮液添加到介电泳芯片上时,PS微球在电极中心区域高效率富集。在负介电泳力辅助下,浓度范围在0.33 amol/mL~2.08 amol/mL的PS微球悬浮液内可形成微球团簇状态。研究结果在分子细胞生物学、药理学和生物化学有潜在的应用前景。

高长宽比金属铝热偶条的制备

金属铝因其与多晶硅具备良好的塞贝克系数差且成本低在红外热电堆中常用作热偶条,热偶条制备在MEMS工艺流程制备中至关重要,其结构形貌对热电堆性能有很大影响。为研究不同制备方法对铝热偶条的形貌及性能影响,本实验采用金属刻蚀工艺、剥离工艺进行热偶条制备,调整溅射功率、光刻胶厚、曝光剂量、超声功率等参数对制备工艺进行优化,通过共聚焦显微镜、扫描电子显微镜及台阶仪表征形貌,半导体分析仪表征电阻值。实验表明:通过ROL-7133负胶,前烘1 min 30 s,曝光剂量85 mj/cm,中烘1 min 40 s,显影48 s,采用金属剥离工艺制备得到了宽度3μm,厚度0.4μm的高长宽比金属铝热偶条,且整体形貌良好,器件电阻值符合要求。

“探测器级”单晶金刚石材料生长技术研究进展

为了获得高性能单晶金刚石探测器,综述了一种制备高质量单晶金刚石的方法。在制备过程中,尝试使用了Lift-off剥离技术,使衬底可重复利用,大大降低了金刚石材料的成本。研究表明,通过该方法制备的金刚石材料质量优于商用"电子器件级"金刚石;利用该类材料制作的金刚石探测器性能优异:对14 Me V中子和5.486 Me Vα粒子的能量分辨率分别达到1.5%和0.3%,电荷收集效率接近100%。

Tensionless contact of a finite circular plate

A general formulation is developed for the contact behavior of a finite circular plate with a tensionless elastic foundation. The gap distance between the plate and elastic foundation is incorporated as an important parameter. Unlike the previous models with zero gap distance and large/infinite plate radius, which assumes the lift-off/separation of a flexural plate from its supporting elastic foundation, this study shows that lift-off may not occur. The results show how the contact area varies with the plate radius, boundary conditions and gap distance. When the plate radius becomes large enough and the gap distance is reduced to zero, the converged contact radius close to the previous ones is obtained.