Technology directions in the field of large-area and low-temperature electronics focuses on lowering the cost-per-unit-area, instead of increasing the number of functions-per-unit-area that is accomplished in crystalline Si technology according to the well-known Moore’s law.
A clear breakthrough in research for large area electronics in the last decade has been the development of thin-filmtransistor, or TFT processes with an extremely low temperature budget of (<150°C) enabling manufacturing of flexible and inexpensive substrates like plastic films and paper.
The materials used for these developments have for a long time been carbon-based organic molecules like pentacene with properties of p-type semiconductors. More recently, air-stable organic n-type semiconductors and amorphous metal oxides, which are also n-type semiconductors, have emerged. The most popular metal oxide semiconductor is amorphous Indium Gallium Zinc Oxide, or IGZO, but variants exist, such as Zinc Oxide, Zinc Tin Oxide, and so on. The mobility of n- and p-type organic semiconductors has reached values exceeding 10 cm2Vs, which is already at par or exceeding the performance of amorphous silicon. Amorphous metal oxide transistors have typical charge carrier mobility of 10 to 20 cm2/Vs. Operational stability of all semiconductor materials has greatly improved, and should be sufficient to enable commercial applications, especially in combination with large-area compatible barrier layers to seal the transistor stack.
In the state-of-the-art p-type only, n-type only and complementary technologies are available. For the latter, all-organic implementations have been shown, but also hybrid solutions, featuring the integration of p-type organic with n-type oxide TFTs. Most TFTs are still manufactured with technologies from display-lines, using subtractive methods based on lithography. However, there is a clear emphasis on the development of technologies that could provide higher production throughput, based on different technologies borrowed from the graphic printing world like screen and inkjet printing. The feature sizes and spread of characteristics of printed TFT technologies are still larger than those made by lithography, but there is clear progress in the field.
The prime application for these TFT families are backplanes for active-matrix displays, including in particular flexible displays. Organic TFTs are well-suited for electronic paper-type displays, whereas oxide TFTs are targeting OLED displays. Furthermore, these thin-film transistors on foil are well-suited for integration with temperature or chemical sensors, pressure-sensitive foils, photodiode arrays, antennas, sheets capable of distributing RF power to appliances, energy scavenging devices, and so on, which will lead to hybrid integrated systems on foil. Early demonstrations include smart labels, smart shop shelves, smart medical patches, etc. They are enabled by a continuous progress in the complexity of analog TFT circuits targeting the interface with sensors and actuators, to modulate, amplify and convert analog signals as well as progress in digital TFT circuits and non-volatile memory to process and store information.
In line with this trend, ISSCC 2013 features three papers representing the latest state-of-the-art of organic thin-film transistor circuits. A front-end amplifier array for EMG measurement is demonstrated for the first time with organic electronics in paper 6.4. Transistor mismatch and power consumption of the amplifier are reduced by 92% and 56%, respectively, by selecting and connecting the transistors trough a post-inkjet printing. Papers 6.5 and 6.6 present advances in analog-to-digital converters for sensing applications. Papers 6.5 demonstrates the first ADC that integrates on the same chips resistors and printed n and p-type transistors. The ADC achieves an SNDR of 19.6dB, SNR of 25.7dB and BW of 2Hz. In Papers 6.6, an ADC made only with p-type transistors is presented that has the highest linearity without calibration and that is 14 times smaller than previous works using the same technology.
This and other related topics will be discussed at length at ISSCC 2013, the foremost global forum for new developments in the integrated-circuit industry. ISSCC, the International Solid-State Circuits Conference, will be held on February 17-21, 2013, at the San Francisco Marriott Marquis Hotel.