Interface Engineered Organic Thin-Film Transistors
Organic thin-film transistor (OTFT)-based electronics performing simple operations/functions offer unique attractions compared to traditional inorganic electronics including lightweight mechanical flexibility and inexpensive large-area coverage and integration. Although speed may be modest versus Si- and inorganic-based circuits, OTFT-based electronics are attractive for diverse new ubiquitous printed electronics applications such as flat-panel displays, sensor arrays, smart cards, and radio-frequency identification (RFID) tags. For OTFTs to be competitive for use in these applications, semiconductor, dielectric, and electrode components should ideally be fabricated via high throughput, low-temperature solution-processing methods such as spin-coating, casting, or printing. In addition, significant performance hurdles must be addressed including, the large operating voltages (>20 V) required to drive moderately complex OTFT circuits, and incompatibilities at material interfaces (organic/organic, organic/metal, and organic/oxide) which strongly influence and in many cases dictate the subsequent device level performance.
Shown here is the development of a series of materials, processes, and device architectures utilizing multifunctional organo-phosphonate self-assembled monolayers (SAMs) which enable low-driving voltage and high electrical performance OTFTs. Rationally designed and integrated SAMs are shown to effectively control the chemical, electrical, and morphological properties at both semiconductor/dielectric and semiconductor/electrode interfaces. These SAM material systems are processed by solution deposition, at low-temperature, in ambient conditions, and are compatible with plastic substrates. The studies presented here are: (1) SAM/high- k metal oxide hybrid gate dielectrics with low-leakage current (-1 nA/cm2) and high capacitance (>400 nF/cm2) providing high-performance OTFTs with driving voltages below 3 V, (2) development of an efficient process for patterning and spin-casting SAM dielectrics on metal oxide activated silicon substrates which enables subsequent fabrication of self-organized patterned solution processed low-voltage OTFTs, and (3) single-component SAMs shown to simultaneously and uniformly modify both metal electrodes and dielectric surfaces to provide desirable interfaces for high-performance bottom-contact OTFTs. Together, these findings represent advancement towards developing low-cost solution processed/printed organic-based electronics.
0794: Materials science