Fullerene field-effect transistors with high on/off ratio
In organic electronics, most of the investigated materials show p-type behaviour. For a complementary logic, also n-type semiconductors are needed. C60 is one of the most promising n-type materials.
Organic field-effect transistors (OFETs) with ordered and nanostructured C60 fullerene layers were prepared by thermal evaporation. P-doped Si wafers were used as substrates in a back gate geometry. The 120 nm thick gate oxide was thermally oxidised, gold contacts with supporting nickel layer were structured by a lift-off proc-ess. The channel length (L) was varied from 1 µm to 10 µm, the channel width (W) from 10 µm to 1000 µm. C60 layers from 50 nm to 300 nm were deposited by PVD from a Knudsen cell and measured in situ without breaking the vacuum.
The OFETs with ordered fullerene layers show clear n-type behaviour. Typical output characteristics for a transistor with L = 5 µm and W = 200 µm and a 50 nm thick C60 layer are shown in the figure. A pre-deposition plasma treatment of the substrate leads to low leakage currents, resulting in high on/off ratios of 105. A charge carrier mobility of µ = 0,2 cm2/(Vs) was found, estimated from transfer characteristic measurements. The C60-FETs show a threshold voltage of Vth = +17 V and an inverse sub-threshold slope of S = 1.5 - 2 V/dec. Electrochemical nanostructuring in ionic liquid (0.1M LiTf2N in EMMIMTf2N) of the fullerene layers in the OFET leads to a decrease of the threshold voltage below +7 V.
Prof. Lothar Dunsch
Organic field-effect transistors (OFETs) with ordered and nanostructured C60 fullerene layers were prepared by thermal evaporation. P-doped Si wafers were used as substrates in a back gate geometry. The 120 nm thick gate oxide was thermally oxidised, gold contacts with supporting nickel layer were structured by a lift-off proc-ess. The channel length (L) was varied from 1 µm to 10 µm, the channel width (W) from 10 µm to 1000 µm. C60 layers from 50 nm to 300 nm were deposited by PVD from a Knudsen cell and measured in situ without breaking the vacuum.
The OFETs with ordered fullerene layers show clear n-type behaviour. Typical output characteristics for a transistor with L = 5 µm and W = 200 µm and a 50 nm thick C60 layer are shown in the figure. A pre-deposition plasma treatment of the substrate leads to low leakage currents, resulting in high on/off ratios of 105. A charge carrier mobility of µ = 0,2 cm2/(Vs) was found, estimated from transfer characteristic measurements. The C60-FETs show a threshold voltage of Vth = +17 V and an inverse sub-threshold slope of S = 1.5 - 2 V/dec. Electrochemical nanostructuring in ionic liquid (0.1M LiTf2N in EMMIMTf2N) of the fullerene layers in the OFET leads to a decrease of the threshold voltage below +7 V.
| Output characteristics of a C60 field-effect transistor with 50 nm fullerene layer deposited at 353 K, measured at room temperature under vacuum. |
Contact
Prof. Lothar Dunsch
| Address: | IFW Dresden |
| Helmholtzstraße 20 01069 Dresden |
|
| Germany | |
| Phone: | +49 351 4659 660 |
| Fax: | +49 351 4659 811 |
| Email: | L.Dunsch@ifw-dresden.de |