互联网、大数据、人工智能等新兴产业的蓬勃发展推动了电子器件微型化,为使其更好地融入日常生活,将具有供能、感知、计算、通信、执行、显示等功能的电子元器件和纺织纤维或制品无缝集成的电子织物引发了人们的极大兴趣。目前电子织物集成方法有3种:1)通过缝纫、刺绣等方式将电子器件直接嵌入纺织品,但织物穿着舒适性会严重降低[1-2];2)通过丝网印刷、喷墨打印、微滴喷射等技术在织物表面集成电子器件和柔性电路,然而,多孔、蓬松织物表面粗糙度高,对高分辨率和长距离条件下印刷均匀致密的多功能电子织物,具有巨大挑战[3];3)将导电功能改性纤维材料通过机织、针织、编织等方式织造集成为电子织物,该方法在满足穿着舒适性前提下可实现复杂电子织物系统大面积集成[4-5]。
作为电子电路信号处理和运算的基本元器件之一,晶体管主要由源电极、漏电极和栅电极组成,通过调节栅极电压来控制源漏电极间沟道电流变化,实现器件开态和关态转变,是电子织物的核心组件。传统的晶体管器件大都以柔性透明聚合物薄膜为衬底,通过磁控溅射、热蒸发、悬涂等技术将金属电极、半导体层、介电层等逐层沉积在衬底表面。器件制备工艺复杂,柔性、透气性不佳。纤维材料质轻柔软、形态多样和易于功能化的优点使其成为制备电子织物晶体管的首选材料。2003年Lee等[6]首次提出采用光刻和涂层技术在纤维表面沉积场效应晶体管(FET),然而,薄膜晶体管制备材料、工艺与多孔、可高度变形的纺织基材难兼容,器件机械鲁棒性不佳。随后Mahiar等[7]提出以聚酰胺纤维为基材通过浸泡聚3,4-乙撑二氧噻吩/聚苯乙烯磺酸盐(PEDOT:PSS)溶液制备纤维电极,再通过凝胶电解质将2根纤维组装成十字交叉结构有机电化学晶体管(OECT),通过编织集成的纤维基OECT(FOECT)逆变器可实现通用逻辑操作。
以上述2种纤维基FET和纤维基OECT晶体管为例,本文简述了近十年来纤维晶体管器件在智能可穿戴和植入式生化传感器、忆阻器和人工突触类脑计算神经形态器件、逻辑电路等领域的最新研究成果;分析了纤维晶体管在器件集成、性能优化和实际应用等方面遇到的问题与挑战以及在电子织物、神经接口等领域的应用前景。
1 纤维晶体管
1.1 纤维基场效应晶体管
纤维基FET器件结构如图1(a)所示。纤维基FET通常是以单根金属纤维为衬底,通过层层堆叠技术将电极、绝缘层和半导体层沉积在纤维表面形成的三端器件,具有体积小、质量轻、热稳定性好、工作区间宽等优点[13]。相较于无机FET,有机FET器件材料来源更广、可低温加工、能耗小且具有更优异的柔性和衬底兼容性,在大面积集成智能可穿戴生化传感器、忆阻器、互补集成电路等领域优势显著。目前,Hwang等[4]通过高分辨率无掩模光刻与毛细管辅助涂层方法将FET、逆变器环形振荡器、光电探测器、信号换能器、分布式温度传感器等多个微型电子器件直接集成在纤维表面制备高密度电子织物。然而,金属衬底亲水性和黏附性有限,如何通过调控材料结构和器件的几何构型来提高器件性能有待进一步探索[14]。
图1
图1
纤维基晶体管器件示意图
Fig.1
Schematic diagram of fiber-based transistors.
(a) Fiber-based field-effect transistor; (b) Fiber-based organic electrochemical transistor
1.2 纤维基有机电化学晶体管
为实现FOECT织造集成,早期Tarabella等[18]尝试以PEDOT:PSS浸渍复合棉纤维为源漏电极、银(Ag)丝为栅极、氯化钠水溶液为电解液,通过缝纫集成在织物衬底表面构筑平行结构FOECT,但器件结构粗糙,响应速率(120 s)慢,机械鲁棒性差。随后Kim等[19]设计了一种双链扭转结构FOECT,其中源漏电极由2根聚多巴胺和P3HT半导体聚合物改性金丝(Au)扭结而成,Au纤栅极通过凝胶电解液间隔层缠绕在源漏纤维表面,最后在FOECT表面涂覆聚氨酯弹性体封装层,器件经反复弯曲变形和强洗涤剂清洗后,仍保持良好电学稳定性,有望推动电子纺织品实际应用,但器件难以大规模生产。近期,有较多学者[20⇓-22]发现借助机织织造技术将源漏电极和栅电极分别作为经纱和纬纱可实现FOECT大面积集成。同时,纤维在不同弯曲半径下具有稳定电学性能,为实现基于FOECT的电子织物奠定了良好的基础。
2 纤维晶体管生化传感器
随着智能可穿戴技术的蓬勃发展和全球人口老龄化加剧,人们对可实时监测生理健康状态的传感器需求与日俱增。与其它生理信号检测方法相比,晶体管独特的信号放大功能,高灵敏度、快响应速率和易于集成等优点使其在生物传感领域备受关注。
2.1 可穿戴生化传感器
生化传感器是一种用于检测和分析生物或化学物质的器件。当待测生化物质接触到OECT生化传感器栅电极表面识别元件(如酶、抗体、核酸等)时将发生特异性反应,栅电极表面电学性能改变产生法拉第感应电流,引起器件有效栅电压变化,根据晶体管沟道电流计算公式[16],Ids随着有效栅电压增加而降低。通过建立电学性能与待测生理标志物浓度间数量关系实现传感功能。
图2
图2
智能可穿戴纤维晶体管生化传感器
Fig.2
Fiber-based transistor for wearable biochemical sensors. (a) FOECT-based glucose sensor; (b) FOECT-based multifunctional biochemical sensors
Wang等以聚酰胺纤维为基材,通过复合二维氧化石墨烯膜亲水模板在纤维电极表面合成纳米线状结构PPy,制备出垂直结构FOECT葡萄糖传感器[16];进一步调控氧化石墨烯片层厚度,Wang等构筑出一种纳米网状和花状复合结构纤维电极,在栅电极表面修饰不同特异性酶,实现FOECT多功能生化传感器,器件检测下限低至1 nmol/L[12]。随后通过调整复合模板组分(如亲水性纳米纤维膜、还原氧化石墨烯膜、碳纳米管(CNT)等)制备出一系列高性能FOECT金属离子[17]、葡萄糖[16]、多巴胺[26]和乳酸[27]传感器,器件灵敏度高,检测下限低。Peng等[28]以聚酰胺纤维为基材,通过逐层沉积Au、PEDOT:PSS等制备源、漏纤维电极,以碳纳米管纤维为栅电极,将3股纤维电极并捻制备一体化FOECT。通过在栅电极表面修饰不同的识别元件实现4种生理标志物传感。然而上述FOECT生化传感器性能与生物识别元件活性密切相关,为避免因酶失活引起的器件失效问题,Wang等[23]提出一种通过分子印记技术改性碳纤维栅极制备无酶FOECT肾上腺素和UA传感器的方法,器件检测下限低至1 pmol/L,重复性好。
2.2 植入式生理监测器件
近年来,OECT优异的柔性、生物相容性、高离子-电子转换效率和稳定的电子-组织界面,使其在神经接口、体内监测、疾病的诊断/治疗中展现出巨大的应用潜力[29⇓-31]。Liu等[32]以CNT修饰的传统针灸针为源漏电极,PANI改性Pt丝为栅电极,制备了一种双针型FET生物传感器,器件具有宽pH值检测区间(4.0 ~ 9.0)且单位pH导致器件有效栅电压变化达53.7 mV,将器件植入固定小鼠脑部,可实时、稳定监测鼠脑pH值动态变化。Fang等[33]以PEDOT:PSS复合聚酰胺纤维为源漏电极、CNT纤维为栅电极,组装成平行结构FOECT,将CNT栅极植入小鼠大脑,展现出良好的生物相容性,可用于实时抗坏血酸(AA)监测。然而,上述刚性金属纤维和碳纤维弹性模量远高于脑组织,二者之间的摩擦将造成脑组织损伤和炎症。为解决上述问题,Feng等[34]采用同轴湿法纺丝技术制备了一种弹性模量((3.15 ± 0.05) kPa)接近脑组织的皮(海藻酸钠)芯(PEDOT:PSS)结构复合纤维。该全聚合物FOECT具有良好的抗生物污染性能,可连续14 d稳定检测小鼠脑部AA变化。
3 纤维晶体管类脑计算器件
图3
图3
纤维晶体管忆阻器和人工突触器件
Fig.3
Fiber-based transistor for memristor and artificial synaptic device.(a) Fiber-based memristor; (b) Artifical synaptic device
3.1 忆阻器
忆阻器是记忆电阻器的简称,不同于电阻器,忆阻器在断电后仍能保持该电阻值,将高电阻和低电阻状态分别定义为二进制1和0,通过电阻变换实现数据存储和计算。相较于薄膜型忆阻器,纤维基忆阻器常见结构包括长丝状和经纬交织状,而在纤维电极曲面构筑高性能忆阻材料和稳定功能界面是制备高性能纤维基忆阻器的关键。Kang等[13]通过调控溶液黏度并引入毛细管辅助涂层工艺在Ag纤维表面沉积有机场效应晶体管实现丝状结构忆阻器,器件可缝纫集成于弹性织物衬底表面,展现出优异的弯曲稳定性且信号存储时长超13 d。然而,器件工作电压(5 V)高,能耗大。Xu等[36]提出利用脱氧核糖核酸(DNA)的亲和性和定向排列结构,在Ag纤维表面电聚合具有取向纳米结构的DNA/Ag纳米颗粒有源层,再与Pt纤维交织成为忆阻器。通过优化银离子(Ag+)传输通道,降低器件工作电压(0.3 V)和功耗(0.1 nW),实现发光电子织物信息处理。Liu等[37]受突触膜离子纳米通道启发选用高离子迁移率、结构稳定的硫化锌铜(CuZnS)纳米片为记忆媒介,通过电聚合在Pt纤维沉积1层具有纳米通道结构的CuZnS薄膜,与Ag丝交织集成,利用纳米通道的活性硫缺陷锚定Ag+并限制其迁移,实现了超低工作电压(89 mV)和功耗(0.1 nW)。该织物型忆阻器可承受数百次弯曲和滑动变形并与供电、传感、显示等无缝集成,实现脑电波等复杂的生理数据高精度(95%)识别与处理。近年来,尽管纤维基忆阻器在功耗、响应速率和循环稳定性等方面均已取得明显提升,但与人脑单个神经突触的超低能耗(1~100 fJ)相比,仍有待进一步研究。
3.2 人工突触
相较于两端忆阻器,三端OECT器件因其水性工作环境、类生物突触的离子-电子传输特性和并行处理优势,在类脑神经形态器件领域展现出巨大优势。为模拟神经纤维结构,国内外研究员尝试在源-漏极之间沉积纤维状有源材料,如纳米纤维膜[38⇓-40]、纳米单丝[41-42]或纳米线[43],此类突触器件功耗可低至1~100 fJ,然而纤维材料与薄膜基底结合力差,器件力学稳定性不佳。Ham等[44]提出以Ag丝为基材借助毛细血管辅助涂层技术在其表面直接构筑铁电突触单元,器件在6 000次重复输入刺激和不同机械弯曲应力下仍具有良好的突触可塑性。由935突触单元组装成的电子纺织神经网络对心电图识别率高达70%,但铁电材料高极化电压(30 V)严重制约其应用。Kim等[45]以双股并捻羧酸功能化P3HT复合Au丝和Au丝分别为源漏电极和栅极设计了一种垂直结构类树突网络状FOECT,其信噪比相对于同尺寸平面型OECT高1.9倍,但功耗高达4 pJ。Wang等[14]以聚酯纤维为基材,通过在纤维表面构筑高离子传输速率的纳米网状结构PPy纤维电极,降低了FOECT器件工作电压(1 mV)和功耗(0.85 pJ), 同时该器件对炎症因子C反应蛋白具有良好的生物传感性能,质量浓度监测范围为10 pg/mL ~ 0.2 mg/mL。综上所述,高性能纤维基人工突触器件仍有巨大探索空间。
4 纤维晶体管逻辑电路
逆变器是逻辑电路的基本组成模块,可将直流电能转变成交流电。早期电阻式阶梯晶体管逆变器主要通过调控栅极偏压改变逆变器开和关状态,随着材料和集成技术发展,目前基于晶体管的逻辑电路可满足更复杂的“与”“或”“非”计算[46]。为提高电子织物的集成度与功能性,研发基于P型和N型纤维电极的互补逻辑电路已成为发展趋势。Jo等[47]提出以PEDOT:PSS和聚酰亚胺(PEI)解掺杂PEDOT:PSS分别为P型和N型半导体材料,通过湿法纺丝制成纤维电极,再缝纫集成于织物衬底表面制备P型和N型OECT逆变器。2种逆变器均成功地将输入信号转换为相应的输出信号,并实现信号放大功能,在纤维逻辑电路领域展现出巨大应用前景。Yang等[5]设计了一种非印刷集成电路纺织品,通过编织集成方式将FOECT、传感器、光电转换-能源储能系统集于一体。该织物集成电路具有卓越的弯曲和拉伸稳定性,可实现“与”“或”“非”等通用逻辑操作并用于无线生物医学监测和早期预警。织物集成电路复杂的功能连接线是限制其发展的重要因素之一,因此开发能够在单一纤维表面高度集成的微型电子系统十分必要。Zhong等[48]利用表面光刻技术和涂层技术在PEI纤维表面实现了沟道长度小于100 μm的OECT精密加工,通过沉积P型和N型半导体材料,在同一根纤维上集成P型和N型FOECT。借助机织和针织集成技术编织成互补逆变器且器件集成“与非”和“或非”通用逻辑门电路,展现出良好重复性。
5 结束语
近年来,纤维基智能可穿戴电子器件随多学科交叉融合迅速发展,集供能、传感、通信、显示和逻辑电路为一体的电子织物备受瞩目。纤维基晶体管因其响应速率快、工作电压低、离子-电子转换效率高、生物相容性好、柔软、透气等优点在智能可穿戴生化传感、生理标志物体内监测、类脑神经形态计算和逻辑电路等领域取得了一系列突破性进展,为实现高度集成多功能电子织物奠定了良好基础。然而,现有薄膜型器件材料、工艺难以满足多孔、曲面纤维电极的制备需求;纤维电极与生物组织之间的机械失配、炎症和生物污染等问题影响长期监测结果准确性;类脑神经形态器件结构、能耗和突触可塑性仍与大脑存在明显区别;晶体管的逻辑电路仅可满足基本逻辑计算,难以处理复杂多元信息。高性能纤维基晶体管器件仍有待继续探索。
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DOI:10.1021/acssensors.3c00415
PMID:37357404
[本文引用: 1]
Local pH of the brain microenvironment is a prominent indicator for assessing health status and is closely related to many diseases; therefore, the development of effective in vivo pH methods is of great importance. This work demonstrates a dual-needle biosensor based on a solution-gate field-effect transistor (FET) for selective and sensitive monitoring of pH in cerebrospinal fluid in the central nervous system. The sensor consists of two parts: a needle FET modified with high-purity carbon nanotubes for electrical signal conduction and a needle gate modified with polyaniline for specific pH response. Based on the device's specific shape and sensing characteristics, the dual-needle sensor is sensitive to the measurement of pH in the living brain while maintaining excellent stability. The prepared dual-needle biosensor exhibits a high Nernstian response of 53.7 mV/pH over a wide pH range from 4.0 to 9.0 and excellent selectivity toward pH against other potential interfering species in the brain. Either in the case of directly injecting weak acids and bases into the rat brain or in the constructed acute acid-base poisoning model, the dual-needle biosensor can respond sensitively to the pH changes of the rat brain. This work has produced a unique dual-needle FET biosensor with high reliability and stability, which provides a new method for real-time monitoring of dynamic pH changes in the body.
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