Solution-based fabrication promises to be an inexpensive and effective means of producing integrated circuits on flexible substrates for a variety of applications, since it will allow the use of ultra low cost printing-based fabrication methods. In order to develop a successful solution-based manufacturing technology, we need access to materials analogous to soluble conductors, dielectrics, and semiconductors. In this project, we are developing a library of such materials, and applying them to various device and circuit architectures. Conductors are a necessary element for device contacts, interconnects, capacitor plates, and inductive elements. We form highly conductive films from solutions that can be deposited on a variety of materials. In order to achieve this we have taken advantage of the low anneal temperatures associated with nano-crystals. We have already developed ink-jet printable gold nano-crystals that, upon anneal at 120 C, result in extremely low-resistance conductive films. We have also developed novel syntheses for silver and copper nano-crystals to be used in similar applications.
Development of suitable dielectrics is another key challenge to the solution-based manufacturing of devices and circuits. Both high-K and low-K dielectrics are needed for device gating and passivation respectively. We are currently developing novel, solution-based materials for the formation of Hafnium, Zirconium, Titanium, and Aluminum oxides as high-K dielectrics, and polyimide-based passivation dielectrics.
The development of a soluble high-performance semiconducting material is perhaps one of the greatest challenges facing the solution-based manufacturing of circuits. Prompted by recent efforts in the field, we are exploring the development of a soluble precursor of pentacene . This modified pentacene molecule is soluble in a variety of solvents, and efficiently converts to pentacene, itself, upon mild heating. We have already manufactured organic FETs using these molecules and are in the process of further enhancing this technology.
Organic transistors show marked sensitivity to chemical compounds over their silicon counterparts. While in the past this may have been regarded as a disadvantage, it is possible to leverage this response by designing chemical sensors based on organic TFTs. Since it is has been shown that transistor drain currents are affected by exposure to various chemical analytes , it is possible to design an array of TFTs that would register unique signatures to different chemical agents and gases.
In this work, we are interested in designing chemical sensors capable of positively identifying a specific chemical agent or gas as well as an integrated approach to fabricating these devices. The development of these sensors will occur in several areas including materials, fabrication, and systems design. It involves understanding the responses of the active materials to an assortment of analytes and tailoring their chemistry to attenuate these responses. For a fully integrated approach, it is also necessary to develop the supporting circuitry, derived from organic materials, which would integrate the sensors’ responses and provide electrical readout. Finally, a solution-based process that is compatible with our in-house inkjet technology will augment functionality by integration into areas such as cloth or food packaging.
While organic semiconducting materials show promise in the realm of low cost/large area applications, the performance of these materials remains low when compared to that of traditional inorganic semiconductors. Certain approaches, however, may improve characteristics such as the field-effect mobility exhibited by current organic semiconductors.
This work seeks to improve the performance of organic semiconducting devices with various techniques, through both device design and organic synthesis. Device scaling is to be utilized to study nanometer scaled organic devices in order to investigate transport mechanisms. Synthetic chemistry will then be attempted to create devices with increased molecular ordering and functionalized integration. Overall this project seeks to drive toward molecularly scaled organic FETs utilizing principles of self-assembly and material integration.
Conventional ICs still suffer from certain incremental costs and are limited to silicon substrates, thereby preventing them from becoming more ubiquitous in consumer applications. Organic-based semiconductors have the advantage of being processed in solution allowing for them to be sprayed or dispensed on a plethora of compatible substrates, including paper, plastic, cloth, and glass. While many organic semiconductors so far do not exhibit the same performance as their silicon counterparts, the advantage of solution-based processing can save costs and allow for widespread integration, making them ideal materials for low-cost electronics.
In this work, we are developing the technology to make ASICs for a variety of innovative and integrated applications. Specifically, the work incorporates several areas of development: (1) the inkjet technology for dispensing and patterning the necessary materials; (2) organic-based molecules for the semiconducting material; (3) advanced materials such as nanocrystals to be used for interconnects and dielectrics; and (4) an integrated, additive process that is also substrate tolerant. We have made progress in multiple areas and are developing a fully integrated process for active devices. Such a process would be used to fabricate RF ID tags, chemical sensors, transducers, or displays on flexible and novel substrates, such as plastic or cloth.