Low Voltage Organic Thin Film Transistor Fabrication
Rafi, Md Nazmul Anam (2020)
Rafi, Md Nazmul Anam
2020
Degree Programme in Electrical Engineering, MSc (Tech)
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2020-02-19
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202002152109
https://urn.fi/URN:NBN:fi:tuni-202002152109
Tiivistelmä
Printed and flexible circuitry has vast potential for novel applications in fields such as sensing and body measurements, due to the simple processes and the possibility of integration of sensor and circuitry using the same production processes. However, there are numerous issues inhibiting the use of such circuitry, including the issue of relatively high voltage operation and the need for low voltage, low power complementary circuitry. Solution-processed n-type metal oxide TFTs operating at low voltage have been reported in few papers, although work to reduce the processing temperature is still on-going. While high mobility p-type organic materials have been available for some time, the operating voltages are still relatively high. The availability of reliable and low operating p-channel organic FETs will foster the development of fully solution-processed integrated circuits.
In this work, low-voltage organic TFTs with dimension characteristics of (W=1000µm and L=80µm), were produced on glass which is cheap and widely available. A bottom gate bottom source-drain (S/D) structure was used. The gate was made of 100nm of evaporated aluminium. ~12 nm thick high-k dielectric layer (Al2O3) was obtained by electro-chemical anodization of aluminium in a 0.01 M solution of Citric Acid at room temperature, under a current density of 105 µA/cm2. The S/D electrodes were made of a 100nm layer of evaporated Silver, modified by treatment with a self-absorbed monolayer (SAM) to improve charge injection. We used a commercial SP400, Merck), organic semiconducting material as active layer. It was deposited by spin coating at 500rpm for 15 seconds and 1200rpm for 120 seconds. Unlike the previously reported operation voltage of 30V using the same material, we demonstrated devices working below the low drain bias voltage of -3 V. We achieved an ON/OFF current ratio of 103; a turn-on and threshold voltage (Vth) of -1.4V. The hole mobility is found to be 0.01cm2/V.s. The results show promise for further development and optimization of the p-channel OTFTs. This may lead to printed circuitry on flexile substrates instead of glass to provide application in several sectors.
In this work, low-voltage organic TFTs with dimension characteristics of (W=1000µm and L=80µm), were produced on glass which is cheap and widely available. A bottom gate bottom source-drain (S/D) structure was used. The gate was made of 100nm of evaporated aluminium. ~12 nm thick high-k dielectric layer (Al2O3) was obtained by electro-chemical anodization of aluminium in a 0.01 M solution of Citric Acid at room temperature, under a current density of 105 µA/cm2. The S/D electrodes were made of a 100nm layer of evaporated Silver, modified by treatment with a self-absorbed monolayer (SAM) to improve charge injection. We used a commercial SP400, Merck), organic semiconducting material as active layer. It was deposited by spin coating at 500rpm for 15 seconds and 1200rpm for 120 seconds. Unlike the previously reported operation voltage of 30V using the same material, we demonstrated devices working below the low drain bias voltage of -3 V. We achieved an ON/OFF current ratio of 103; a turn-on and threshold voltage (Vth) of -1.4V. The hole mobility is found to be 0.01cm2/V.s. The results show promise for further development and optimization of the p-channel OTFTs. This may lead to printed circuitry on flexile substrates instead of glass to provide application in several sectors.