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Ambipolar transistors Ambipolar transistors: Organic integrated circuits might be used in low-cost high-volume applications such as contactless RFID transponders, or electronic barcodes, in drivers for flexible displays, and in smart sensors, or electronic noses. Although one might call these low-end devices, application is hampered because the minimum requirements presently cannot be met. For instance, the transponders require a higher operating frequency, and the display drivers need reduced power consumption. Other envisaged applications require an integration level that cannot yet be met; with an increase of the complexity the yield decreases.
The problems are related to the type of logic being used. Present organic field-effect transistors operate mainly in a hole accumulation mode.The transistors can only be combined into unipolar, PMOS, logic circuits. Similar as in standard silicon industry, CMOS logic is required. The advantages are higher operating frequencies, low-power dissipation and good noise margin. The improved noise margin will allow more complex integrated circuits with robust operation. Research objectives and relevance to technology; The research objective is to demonstrate organic complimentary logic gates. A boundary condition for polymer electronics is that the final devices should be low-cost. Hence, we aim for a transistor lay-out that is as simple as possible. The use of more than one semiconductor, and more than one type of electrode has to be avoided. Here we will demonstrate CMOS logic circuits using a single semiconductor and a single type of electrode. References: 1. E. C. P. Smits, T. D. Anthopoulos, S. Setayesh, E. van Veenendaal, R. Coehoorn, P. W.M. Blom, B. de Boer, D. M. de Leeuw, “Ambipolar Charge Transport in Organic Field-effect Transistors” Phys. Rev. B, 73, 205316-1–205316-9 (2006). Ferroelectric memories New non-volatile memories are being investigated in order to keep up with the organic electronics road map. Ferroelectric polarisation is an attractive physical property as the mechanism for non-volatile switching, since the two polarisations can be used as two binary levels. However, in ferroelectric capacitors the read-out of the polarisation charge is destructive. The functionality of the targeted memory should be based on resistive switching. In inorganic ferroelectrics conductivity and ferroelectricity cannot be tuned independently. The challenge is to develop a storage medium in which the favourable properties of ferroelectrics such as bistability and non-volatility can be combined with the beneficial properties provided by semiconductors such as conductivity and rectification. In this thesis an integrated solution is presented by blending semiconducting and ferroelectric polymers into phase separated networks. The polarisation field of the ferroelectric modulates the injection barrier at the semiconductor–metal contact. The combination of ferroelectric bistability with (semi)conductivity and rectification allows for solution-processed non-volatile memory arrays with a simple cross-bar architecture, where the logic table of the array is constructed and is read-out non-destructively. The concept of tunable injection barrier is successfully employed to address the organic light emitting diodes in a matrix display. References: 1. R.C.G. Naber, C. Tanase, P.W.M. Blom, G.H. Gelinck, A.W. Marsman, F.J. Touwslager, S. Setayesh and D.M. de Leeuw, “High Performance Solution-processed Polymer Ferroelectric FETs” Nature Mater., 4, 243–248 (2005). 2. R. C. G. Naber, M. Mulder, B. de Boer, P. W. M. Blom, D. M. de Leeuw, “High Charge Density and Mobility in Poly(3-hexylthiophene) Using a Polarizable Gate Dielectric” Org. Electr., 7, 132–136 (2006). 3. R. C. G. Naber, B. de Boer, P. W. M. Blom, D. M. de Leeuw, “Low-Voltage Polymer Transistors for Nonvolatile Memories” Appl. Phys. Lett., 87, 203509-1–203509-3 (2005). |
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Molecular Electronics - Physics of Organic Semiconductors - Design©2006 M. Kuik & J.J. Brondijk & B. de Boer