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不同衬底上氮化硼薄膜制备与场发射性质研究
Preparation and Field Emission Characteristics of Boron Nitride Films on Various Substrates
【作者】 冯伟;
【导师】 赵永年;
【作者基本信息】 吉林大学 , 凝聚态物理, 2004, 硕士
【摘要】 氮化硼(BN)是一种性能优异,极具发展潜力和广泛应用前景的新型宽带半导体材料。其晶体主要有两种结构形式:sp~2杂化结构的六角氮化硼(h-BN)和sp~3杂化结构的立方氮化硼(c-BN)。六角氮化硼(h-BN)与石墨碳类似,具有良好的润滑性、导热性及热稳定性,并且是一种非常好的电绝缘材料。h-BN非常适合应用于抗辐射和超高压高温技术领域。有报道表明h-BN还具有高声波传输速率和优良的透光性是作为表面声波(SAW)器件基体的合适材料。立方氮化硼具有非常高的硬度(仅次于金刚石)、很小的摩擦系数、良好的热导率、极好的化学稳定性及高温抗氧化能力。使c-BN能够作为理想的硬质刀具涂层。c-BN薄膜还具有优良的电学性能,如良好的绝缘性、宽禁带,以及最近发现的场致电子发射特性,使其在高温、大功率电子器件,场致电子发射平板显示器等新型电子器件领域具有广泛的应用前景。 很多研究者先后报道了采用射频溅射沉积(RF Sputtering),离子束辅助沉积(IBAD),离子镀(Ion Plating),激光蒸镀(PLD),等离子体辅助化学气相沉积(PACVD)等各种物理和化学气相沉积方法,在真空条件下获得了c-BN或含c-BN相的膜。目前c-BN的合成主要存在以下几个问题:1.成核和生长机理尚不清楚。2.附着力差。3.难以达到理想的化学配比。4.立方相上的界面层和立方相层与衬底之间都有一薄层sp~2键合的氮化硼。影响了其在超硬涂层材料和电子学领域的应用。5.目前用各种方法生长的立方氮化硼薄膜中,立方相的晶粒尺寸很小,一般只有几十纳米,使其应用受到很大限制。 使用射频磁控溅射(RFMS)方法,在钼衬底和镍锰钴衬底上通过改变吉林大学硕士学位论文了沉积参数沉积了一系列氮化硼薄膜。傅立叶变换红外光谱(FTIR)表明,所获得的薄膜结构一致,均为六角氮化硼薄膜。溅射功率、衬底偏压、沉积气压,各种气体的含量、衬底温度和沉积时间等实验参数均对薄膜的生长有一定影响。系统的实验结果表明,沉积氮化硼薄膜较好的条件为:衬底偏压,50V,溅射功率150W,沉积时间1加min,沉积气压4Pa,氮气含量50%,衬底温度500℃。从射频磁控溅射实验的结果来看,沉积在钥衬底上的氮化硼薄膜质量稍好于沉积在镍锰钻合金衬底上的氮化硼薄膜。 采用磁控弧光增强等离子体化学气相沉积(MA一PECVD)方法制备氮化硼薄膜,沉积气压为50~100Pa,N/B流量比为25:l和50:l,衬底射频偏压由OV变化至一150V,衬底温度为900℃,沉积时间为10~30min。经傅立叶变换红外光谱(FTIR)分析,在10A放电电流条件下,得到的薄膜结构均为六角氮化硼(h一BN)。随沉积时间变长,衬底温度增加,N/B流量比增加,薄膜中六角氮化硼含量增加,薄膜结晶度变好。衬底射频偏压对薄膜质量的影响不大。 提高弧光放电的电流,从10A增至18A,薄膜中出现立方相氮化硼 (。一BN),立方相含量随N/B流量比和沉积温度的增加而增加。由此推测,弧光放电的电流密度是影响立方氮化硼合成的重要参量:此外,适当的N旧流量比和衬底温度也对立方氮化硼的成核与生长有促进作用。值得注意的是,在立方氮化硼沉积的过程中,衬底未加偏压。一般认为,高能粒子的轰击是合成立方氮化硼薄膜必不可少的条件。但在使用化学气相沉积方法进行立方氮化硼薄膜合成的研究过程中,很多研究者都在没有高能离子参与反应的情况下生成了c一BN。这表明化学气相沉积(C VD)c一BN的机理可能完全不同于物理气相沉积(PVD)。在实验所使用的BC13一NZ一H:气体系统中,氯原子起着刻蚀薄膜中六角相的作用,而氢吉林大学硕士学位论文可以平衡氯原子的刻蚀能力并能够稳定表面sp,键。 传统的电子发射大都是以某种形式给予电子能量,使之能够越过表面势垒而逸出真空。场致发射(FE)一方面利用外加电场降低表面势垒,而更重要的方面是使表面势垒变薄,使得电子可以隧穿逸出。同时外加电场还可以渗透到材料内部,使其中的电子加速而逸出。场发射器件具有体积小、电流密度大、响应快和效率高等优点。场致发射的主要研究内容一方面是锐化尖锥阵列,另一方面则是优化表面材料,或者是二者的结合。 早期场发射材料多采用金属尖端,其发射机理较清楚,工艺较成熟,但由于金属材料场发射阀值电场较高,面临着被淘汰的局面。当然,用SPindt法制作的金属场发射阵列(F EA)由于其发射特性稳定,是一个可发展的方向;但其技术难度高,工艺较复杂。近年来,一些宽带隙材料作为场电子发射材料崭露头角,如金刚石、类金刚石、氮化铝、碳化硅等一些宽带隙半导体薄膜,因为这些材料具有良好的化学与热稳定性、高熔点、高热导率、高击穿电压及大的载流子迁移率,特别是极小的电子亲和势甚至是负的电子亲和势,大大降低了场发射的阀值电压。最近,在BN薄膜表面发现负电子亲和势,这使之成为平面冷阴极材料的有力竞争者。 将在不同衬底、不同沉积条件下得到的氮化硼薄膜做场发射测试,发现薄膜表面的粗糙度对场发射性能有很大的影响。表面粗糙度大的样品,由于尖端效应,使得表面凸起处曲率大的区域电场增强,从而使表面势垒高度降低,宽度
【Abstract】 Boron nitride has a lot of excellent properties and an extensive application foreground as a kind of wide band gap semiconductor material. It primarily has two kinds of crystalline constructions: sp2 hybridized structurecorresponds hexagonal boron nitride (h-BN) and sp3 hybridized structure rr corresponds cubic boron nitride (c-BN). h-BN is similar with graphite carbon, ,it has good thermal stability, thermal conductivity, good lubricity. So it could be an ideal electrical insulating material. And c-BN is appropriate to be used in radio resistance and ultra high temperature high pressure technique fields. There are some reports that h-BN have a high sound wave transmission velocity and excellent light transmittance. That’s means that it’s a good candidate for surface acoustic wave device substrate. Cubic boron nitride has very high hardness (only smaller than diamond), little friction coefficient, high thermal conductivity, excellent chemical stability and anti-oxidation at high temperature. It enables c-BN an ideal hard tool coating. c-BN film also has extraordinary electrical performance, such as good insulativity, wide band gap and negative electron affinity which was found recently. It have an extension application foreground in high-temperature, large power electrical device and field emission flat display or other new type electrical device. i’A lot of researchers successively report various physical vapor deposition and chemical vapor deposition techniques to obtain c-BN film or film that containing c-BN, such as radio frequency sputtering deposition(RF sputtering), ion beam assisted deposition(IBAD), ion plating , pulse laser ablation deposition(PLD), plasma assisted chemical vapor deposition(PACVD). Atpresent, there are some problems in synthesizing c-BN films: 1. Nucleation and growth mechanism is not very clear. 2. Poorly adhesion. 3. Deviation of stoichiometric composition. 4. Interlayer between cubic phase and substrate and lamella upon cubic phase which is sp2-bonded. This limits the application in super hard coating materials and electrical filed. 5. It is commonly little as a few tens nanometers for c-BN crystal grains grown by various techniques and this restricts its application.We deposit a series of boron nitride films on molybdenum and NiMnCo alloy substrates by changing deposition conditions. Fourier transform infrared spectroscopy (FTIR) indicates that all of films have the same structure of hexagonal construction. It have a strong influence for growth of films such as Sputter power, bias voltage, deposition pressure, gas component, deposition temperature and deposition time. The results of serial experiments indicate that it is good for film growth in such conditions: bias voltage set at -50V, deposition power at 150W, deposition time lasted 120min, total pressure is 4Pa, Na percentage is 50%, substrate temperature set at 500 C. BN films growth on molybdenum substrates have a better quality than films growth on NiMnCo alloy substrates.BN films deposited by magnetron arc plasma enhanced chemical vapor deposition. Deposition pressure have a range of 50~100Pa, N/B flux ratio is 25:1 or 50:1, bias voltage various from 0V to -150V, substrates temperature fixed at 900 C, deposition lasted 10~30min. the structure of as-grown films is found to be hexagonal boron nitride uniformly by FTIR analysis. With longer deposition time, higher substrate temperature and higher N/B flux ratio, crystalline is improved. It is also found that bias voltage have a negligibleeffect on film growth.Cubic phase appeared when arc current was increased from 10A to 18A, it can be concluded that arc current is very important for synthesizing c-BN. otherwise, appropriate N/B flux ratio and substrate temperature can accelerate nucleation and growth of c-BN. it should be noted that bias voltage is free when deposition. It is generally known that bombardment of energetic particles is essential for synthesizing c-BN film, but by research of CVD deposition of c-BN, many res
- 【网络出版投稿人】 吉林大学 【网络出版年期】2004年 04期
- 【分类号】O484
- 【被引频次】5
- 【下载频次】439