Research On Low Voltage Printed Ambipolar Carbon Nanotube Thin Film Transistor And Logic Circuits

Printed electronics has broad potential applications due to its low fabrication cost,compatibility with flexible substrates,and its suitability for applications where large footprints are required.However,the supply voltages of printed circuits are high in general due to limitations of both the electronic properties of printable materials and the coarse dimensions of printed transistors.This thesis aims to realize the low voltage operation of printed circuits by using a printable electrolyte?so-called ion gel?which having an ultra-high specific capacitance?about several tens of?F/cm²?as a gate insulator.Ion gel is a composite formed by self-assembly of ionic liquids in triblock copolymers.Usually,PS-PMMA-PS is dissolved in ionic liquid[EMI][TFSA]solutions to obtain ion gel.These types of ion gel materials and other functional materials,such as semiconductor single-walled carbon nanotubes,conductive nano-silver and gold ink,can be easily used to construct electrolyte-gated transistors?EGTs?and circuits on flexible substrates by aerosol printing.In this thesis,I used ion gels as dielectric layers to construct printed ambipolar carbon nanotube thin film transistors?TFTs?.It has demonstrated that printed ambipolar carbon nanotube TFTs show good performance with low operation voltage and strong environmental radiation hardness.Furthermore,these kinds of TFTs can be applied to high-performance logic gates with high stability.First,the polarity and threshold voltage of printed TFTs are tuned by controlling the concentration of the electron dopant in ion gel ink.High-performance ambipolar TFTs were obtained with an electron dopant concentration of 2 mM in ion gel dielectric layers.Furthermore,CMOS-like inverters with two identical high-performance printed bipolar SWCNT TFTs exhibit high noise margin(NM_H81%/NM_L 62%,at V_DD=0.5 V)and voltage gains(25,at V_DD=0.5 V)at V_DD of 1 V,and they can also work well at Vdd of 0.25 V.To further improve the performance of printed SWCNT TFT devices,the low-voltage high-performance printed ambipolar carbon nanotube TFTs were also achieved when using the a double dielectric layer,i.e.,the ALD deposition of high-k metal oxide thin films as buffer layers prior to printed ion gels.CMOS-like inverters based on such ambipolar SWCNT TFTs showed higher performance,including higher voltage gain,lower power consumption,and larger noise margin,etc..Finally,the radiation hardness of printed SWCNT TFTs and circuits with ion gel as the dielectric layer were investigated.The results show that the printed p-type SWCNT TFTs and CMOS-like inverters using ion gel as the dielectric layer have high stability under radiation environment.For example,printed p-type SWCNT TFTs and circuits can operate normally at high dose rate?560 rad/s?after being irradiated with a total radiation dose of 4 Mrad.Furthermore,performance of printed SWCNT TFTs with double dielectric layers has no obvious changes after being irradiated by a total radiation dose of 3 Mrad,which demonstrates these kinds of printed TFTs have the more excellent radiation hardness.