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2011.12.26 Chun-Chieh Lu Carbon-based devices on flexible substrate 1.

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Presentation on theme: "2011.12.26 Chun-Chieh Lu Carbon-based devices on flexible substrate 1."— Presentation transcript:

1 2011.12.26 Chun-Chieh Lu Carbon-based devices on flexible substrate 1

2 Graphene properties Dimensions - Available in a wide range of platelet lengths (typically 1-20 μm) and thicknesses (approximately 0.34 nm to 100 nm) - Single layer graphene as thin as 0.34 nm Strength - Fifty times stronger than steel - Ultra-high Young’s modulus (approximately 1,000 GPa) and highest intrinsic strength (~ 130 GPa estimated) Conductivity - The highest thermal conductivity known today (up to ~ 5,300 W/(mK), five times that of copper, at a density that is four times lower - Exceptional in-plane electrical conductivity (up to ~ 20,000 S/cm) Transmittance - Absorptance 2.3% for single layer graphene Good performance of strength, conductivity and transmittance  Advantages for transparent and flexible electronics 2

3 3 Carbon-based transparent conducting film (TCF)Carbon-based field effect transistor

4 Carbon-based transparent conducting films (TCFs) Transfer to PETTransfer to glass Transmittance vs. Sheet resistance 4

5 Carbon-based transparent conducting films (TCFs) Graphene films bending and stretching test 5 Compared with ITO film:

6 6 Field-effect transistor in flexible regime: logic gate, portable memory, display driving circuit, electronic tagging, RFID system… Field-effect transistor needed in conventional process: metal contact deposition in high vacuum and gate oxide grown in high temp. process For flexible substrate: (1) To develop low temperature, printing processes for materials that form the channel region, gate insulator and electrodes on soft substrates with high thermal expansion coefficients (2) To overcome intrinsic limitations of mechanical properties associated with conventional materials and circuits through development of new materials or device architectures. For example: High-k inorganic dielectrics (HfO 2, Al 2 O 3 and ZrO 2 ) cannot be available for flexible devices based on plastic substrates due to their high growth temperature.  Due to low temperature and printing process, ion gel can be used as good gate dielectric of carbon-based field effect transistor on flexible substrate Graphene field-effect transistor on flexible substrate

7 poly(styrene- block-methyl methacrylate- block-styrene) (PS-PMMA-PS) triblock copolymer Process: (1)[EMIM][TFSI] : PS-PMMA-PS : solvent = 0.7 : 9.3 : 90 (w/w) (2) Drop-casted onto graphene (3) After the solvent was removed, an ion gel film was formed through physical association. (4) Deposit gate electrodes (shadow mask) 7 Ion gel =+ + solvent + :[EMIM] - :[TFSI] 凝膠

8 Graphene field-effect transistor on flexible substrate Electric double layer (EDL) EDL capacitor with a dielectric of sub nanometer thickness Ion gels provided a specific capacitance of 5.17 μF/cm 2 at 10 Hz FET devices can operate within a low voltage region (~3 V) with a high on- current (~mA) on Si substrate. Due to the ultrahigh capacitance of the ion gel gate dielectric yielded this low-voltage, high-current operation 8 C-V measurement

9 Graphene field-effect transistor on flexible substrate Transfer to PET substrate Hole mobility: 203 ± 57 50 cm 2 /Vs Electron mobility: 91 ± 50 cm 2 /Vs (at V D =-1 V) Only 20% changes in μ/μ o were observed as the bending radius was changed from 6 to 0.6 cm 9 Problem: Low ON/OFF, gate electrode dimensions…

10 Carbon-based logic gate on flexible substrate 10 Graphene : low ON/OFF but easily for large area fabrication CNT: high ON/OFF but complicated fabrication  Using graphene as the electrode and CNT as device channel  All carbon–based field effect transistor on flexible substrate 5 layer graphene as electrode (270 Ω/□) Network SWCNTs as device channel

11 11 Carbon-based logic gate on flexible substrate Using high source-drain current to break metallic CNTs Small hysteresis that is caused by the interface trap states parasitized between the gate electrode and dielectrics Graphene-CNT device showed both a high transmittance of 83.8%, due to highly transparent monolayer graphene for electrodes

12 12 Carbon-based logic gate on flexible substrate Due to the bundle problem of CNTs, the random network CNT channels were optimized as a function of CNT density and channel width The inverter gain was approximately 1.4, and a supply voltage of 0-5 V was enough to provide the switching functions The PMOS inverter consisting of two p- type transistors Reasonable device performance, such as an on/off ratio of approximately 10 3 and a mobility of approximately 81 cm 2 /Vs were achieved at a density of 7.5 SWCNTs μm -1.

13 Carbon-based logic gate on flexible substrate 13 Bending and stretching test

14 Carbon-based materials such as CNTs and graphene have large potential in flexible electronics Due to low temperature and printing process, ion gel can be used as good gate dielectric of carbon-based field effect transistor on flexible substrate Using multilayer graphene as electrodes and network SWCNTs as device channel can achieve the all carbon logic gate circuit for transparent and flexible application 14 Summary


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