【作者】 胡伟；

【导师】 刘式墉； 马春生；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 我们提出利用有机小分子空穴注入材料m-MTDATA来改善金与并五苯表面层之间的空穴注入特性。有机空穴注入材料m-MTDATA具有较低的电离势(Ionization Potential, IP)、良好的成膜性和较高的黑电导率(10-10 S.cm-1),在有机发光二极管(OLEDs)中,它被广泛使用以降低器件的开启电压、提高器件的亮度和效率。本文,我们将m-MTDATA引入有机薄膜晶体管中,通过在与金接触的并五苯表面层中掺入m-MTDATA(比例1:1),有机半导体薄膜的成膜性得到改善,优化了金与有机层间的接触性质,减小了金与有机薄膜表面层之间的接触电阻,提高了源端到有机层的空穴注入能力。相对一般结构的器件,其阈值电压的绝对值由11V降至2.8V,线性区的场效应迁移率由0.16 cm2/Vs增大到了0.51 cm2/Vs;利用掺杂类型的空穴注入层也保证了器件在关态时具有较小的漏电流,当栅压由0V变化到-20V,得到了开关电流比大于104的性能较好的器件,为并五苯薄膜晶体管在低电压下的产业化应用提供了一种可能的方法。我们提出在金与并五苯之间生长一层氧化钼缓冲层,通过优化缓冲层的厚度,来改善金与并五苯之间的接触性质。氧化钼作为一种宽禁带半导体,它的价带位于5.2eV处,与金的功函数和并五苯的HOMO能级匹配得较好。当氧化钼的厚度由0纳米逐步增加到10纳米的时候,缓冲层的作用也逐步体现出来,器件在线性区的场效应迁移率由0.17 cm2/Vs增加到0.68 cm2/Vs,阈值电压的绝对值由13V下降到了5.5V。当缓冲层的厚度由10纳米继续增加时,器件的性能基本保持不变。由于氧化钼缓冲层的加入,避免了金与并五苯之间的高空穴注入势垒和较大接触电阻的问题,实现了较低工作电压下(栅压和源漏电压均较小)的较高迁移率的并五苯薄膜晶体管器件。考虑到热生长的并五苯薄膜一般呈多晶态的性质,我们在并五苯有机薄膜晶体管基本工作原理的基础上,考虑到晶粒间界等对空穴具有的陷阱作用,通过分析有机半导体薄膜中,限域态载流子和自由载流子与薄膜电导率的关系,得到了并五苯薄膜晶体管中,载流子迁移率与栅压相关的结论。我们借鉴多晶硅薄膜晶体管中迁移率与栅压相关的经验公式,估算出了在并五苯有机薄膜晶体管中,场效应迁移率的栅压依赖经验公式中的主要参数γ。介绍了我们自己设计和搭建的有机薄膜晶体管测试系统。我们以2004年4月,美国电气与电子工程师学会(The Institute of Electrical and Electronics Engineers, IEEE)公布的有机薄膜晶体管的标准测试方法为基础,以两个Keithly 2400电流-电压源、电脑、控制软件和数据收集卡为测试设备,利用电脑控制软件对Keithly 2400进行电压变化和电流参数的测量,并利用数据收集卡对所测得的数据进行电脑录入,实现对器件电流-电压特性和数据的准确测试。更多还原

【Abstract】 In the last twenty years, organic electronics based on organicsemiconductor materials and its applications in the information industry havemade rapid progress. The studies on the organic semiconductor devicesinclude organic light-emitting diodes （OLEDs）, organic thin-film transistors（OTFTs）, organic solar cell and organic sensors, etc. And now, OLEDs andOTFTs are on the way to industrialization.The first example of an OTFTs based on polyacetylene was reported inthe literature in 1983. And in 1990, the OTFTs based on short conjugatedoligomer, e.g., sexithiophene, showed a mobility of the order of 10^-1 cm²/Vs,almost matching that of a-Si:H. And now, it has two important applicationsthat OTFTs will be showed in the market, one is the TFT unit device using inthe active matrix driving circuit, especially OTFTs are compatible with theflexible backbone circuit. The other one is the OTFTs can be used in thelow-cost Radio Freqency Identification （RFID）.Most of switch devices in the active matrix circuit driving fiat planedisplay, such as AMLCD, are based on hydrogenated amorphous silicon（a-Si:H） with typical field-effect mobility of 0.5 - 1.0 cm²/Vs and on/offcurrent ratio > 10⁷. However, high performance a-Si:H TFTs require processtemperature > 200℃and therefore it limited compatibility with polymeric substrates.Organic TFTs on the other hand offer an attractive low-temperaturealternative. TFTs based on the organic seminconductor pentacene currentlyshow the best performance for OTFTs with typical field-effect mobility of 1.However, there are some problems should be solved such as stability, highthreshold voltage and high energy consuming etc.Pentacene is a p-type organic seminconductor, and in the vacuumdeposited polycrystalline pentacene film bulk, the free carrier density is verylow and the film is abundant of hole traps. At low gate voltage, most of theholes injected in the semiconductor are trapped into these localized states. Atan appropriately high gate voltage, all trap states are filled and subsequentlyinjected carriers move with the microscopic mobility associated with carriersin the delocalized band. So, the interface characteristic between Au andpentacene play an important role in the OTFT performance. Researchers havestudied the interface property. And they found the gold atom will diffusion intothe pentacene film surface when gold is deposited onto pentacene, there willform an metallic interface which result in the gold surface work function lower0.8eV, and then the hole injection barrier between Au and pentacene increasedto 1 eV which will confine the hole injection and lead to high contact resistance.This thesis reported relative high performance pentacene OTFTs by modifyingthe interface between Au electrodes and pentacene.We introduced the excellent organic hole injection material （HIM）m-MTDATA into the OTFTs, which has been widly used in OLEDs for itsexcellent uniformity, high dark conductance and stability in air. In the interfacelayer contact with Au, we doped HIM in it with ratio of 1:1. the performancesof the OTFTs with HIM are improved, the field-effect mobility increased from0.16 cm²/Vs to 0.51 cm²/Vs,and the absolute threshold voltage valuedecreased from 11V to 2.8V. That is say that with the HIM, the hole injection ability is enhanced and the contact resistance is reduced.Second, we insert a MoO3 buffer layer between Au and pentacene. Whenthe thickness of buffer layer varied from 0 to 10 nm, the performance ofOTFTs increased. The field-effect mobility in the linear region increased to0.68 cm²/Vs and threshold value down to 5.5V, and when the buffer layerthickness increased to 20nm, the performance of the OTFTs is almost samewith 10nm. So, the OTFTs with the buffer layer of 10nm MoO₃ have relativehigh mobility and low operation voltage, this method can be used in theindustry process.Otherwise, we deduced the conclusion that the field-effect mobility of thepentacene-based organic thin-film transistors dependent on the gate voltage.For the high density of hole traps linked to grain boundaries in thepolycrystalline pentacene film, theμ_FET is expected to be much lower thanmicrocosmic mobility. Base on the relation of the mobility and gate voltage,we estimate the parameter of the experience expressions.The last, we introduced the manufacture process of our OTFTs and thetest system based on the IEEE standard test methods for the characterization ofOTFTs, in 2004.更多还原