| Summary: | 碩士 === 國立雲林科技大學 === 光學電子工程研究所 === 95 === In this research, gate oxide metal/insulator/semiconductor (MIS) capacitors and gate oxide organic thin film transistors (OTFTs) are prepared. In the MIS experiments including inorganic/organic insulators. First, we mixed Ba0.7Sr0.3TiO3 (BST) inorganic solution by sol-gel method, and coated it on n-type (100) silicon substrate by spin-coating method, then placed samples in the annealing furnace (with annealing temperature of 100℃, 300℃, 500℃, and 700℃) at oxygenic atmosphere to form the high dielectric constant (high-k) BST insulator. Second, we mixed PHEMA organic solution (weight percentage, Wt%: 2.5% and 5% and 7.5% and 10%) with alcohol, and coated that on n-type (100) silicon by the same spin-coating method, then placed samples in the oven to dry by heat and formed the PHEMA insulator. Finally, we used evaporator to deposit aluminum (Al) electrode above the insulator, then the MIS capacitors are formed.
We used KEITHLEY 236/590 to measure the C-V and J-V characteristics of MIS capacitors and used atomic force microscope (AFM) to analyze the surface state of insulator, then analyzed the effects between different insulators and characteristics of MIS capacitors. The MIS capacitors Al/BST/Si/Al and Al/PHEMA/Si/Al and Al/BST/PHEMA/Si/Al are shown. From the results of one-layer BST insulator’ condition (after annealing 700℃), the best data for average capacitance is 151.21 pF, for dielectric constant (k) is 45.31, for the physical thickness is 130.2 nm. The leakage current density (J = 2.03×10-8 A/cm2) of double-layer PHEMA/BST insulator’ condition (Wt% = 2.5% / after annealing 700℃) is smaller than the one (J = 5.2×10-1 A/cm2) of one-layer PHEMA insulator’ condition (Wt% = 2.5%) about seven order, so the leakage current can be reduced obviously by the high-k BST insulator.
In the OTFT experiment, we analyzed the effects between different insulator’s conditions and characteristics of OTFT devices. The devices have four major layers: gate electrode (Al), gate insulators (BST and PHEMA and PHEMA/BST), organic active layer (Pentacene) and source/drain electrode (Ni).
We used HP4156C analyzer to measure the I-V properties (I¬D-VD and Log|ID|-VD and ID-VG) and used AFM to analyze the surface state of pentacene. Results of the OTFT devices Ni/Pentacene/BST/Si/Al and Ni/Pentacene/PHEMA/Si/Al and Ni/Pentacene/PHEMA/BST/Si/Al are shown. From the results of double-layer PHEMA/BST insulator’ condition (Wt% = 2.5% / after annealing 700℃), the best data for (On/Off current ratio (IOn/IOff) is 94.171, for carrier mobility (μ) is 1.49 cm2/V.s, for threshold voltage (VT) is 1.328 V, for the biggest grain size is 1.08 μm and the largest operation current (IDsat = 5.92 μA) at the same channel’ condition (channel width is 1.5 mm and channel length is 0.1 nm). For the one-layer BST insulator’ condition (after annealing 700℃), the IOn/IOff = 3.485, μ = 0.0362 cm2/V.s, VT = -1.277 V, the grain size is 0.118 μm, and IDsat = 1.86 μA are obtained. For the one-layer PHEMA insulator’ condition (Wt% = 2.5%), the IOn/IOff = 81.138, μ = 0.272 cm2/V.s, VT = 0.85 V, the grain size is 0.637 μm, and IDsat = 3.68 μA are obtained. For the one-layer PHEMA insulator’ condition (Wt% = 10%), the IOn/IOff = 91.071, μ = 2.78 cm2/V.s, VT = 2.91 V, the grain size is 0.677 μm, and IDsat = 4.93 μA are obtained.
According to the results of OTFTs, the gate insulator of OTFT devices fabricated with inorganic and organic materials have the advantages of high carrier mobility in organic material and low leakage current in high-k inorganic material. And bigger grain size of pentacene can be deposited on suitable hydrophobic surface between pentacene and insulator in organic material.
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