以聚乙烯酚和聚乙烯酚-聚甲基丙烯酸甲酯共聚物介電層製成五苯環素有機薄膜電晶體之研究

Abstract

有機薄膜電晶體近年來被廣泛地開發，由於它相當具有潛力應用在低端電子產品，像是可撓式顯示器驅動、互補式電路和射頻辨識。在本研究中，將聚乙烯酚(PVP)和乙烯酚及聚乙烯酚共聚甲基丙烯酸(PVP-PMMA)做為閘極介電層的五苯環素有機薄膜電晶體做研究。PVP是一種常見的介電層由於它的低漏電和高載子移動率，然而PVP元件卻由於顯著的偏壓壓力效應及磁滯效應而引起可靠度問題，和PVP元件相較之下，PVP-PMMA元件卻具有輕微偏壓壓力效應及無磁滯現象，兩元件的差異性可能受到外界環境影響程度的不同。接下來實驗，元件在無水環境中被封裝，和PVP-PMMA元件比起來，PVP元件的載子移動率劇烈地下降，然而兩元件的閘極偏壓效應和遲滯都有效地被抑制，甚至對PVP-PMMA元件對閘極施加負30伏特偏壓一萬秒仍具有初始電性。 基於以上的結論，PVP介電層中的氫氧基對水氣的吸收主導了磁滯效應和電子缺陷的形成。然而PVP-PMMA介電層中的甲基團阻擋了水氣的穿透而避免元件劣化。為了更進一步瞭解水氣的影響，我們製作了多孔結構使得水氣能加速進出PVP表面的速度。當多孔元件在一般環境中量測時，具有高載子移動率及大電流，在氮氣環境下其載子移動率和電流都變得相當的低，這說明了介電層中氫氧基的極化比例大幅影響了通道載子濃度。 新穎的氨氣感測器便基於以上機制而開發，感測器在氮氣環境中操作使得PVP的氫氧基保持電性中和，隨著氨氣氣體的進入時，氫氧基便從氨氣獲得電子進而帶負電感應出額外的電洞載子。該元件能隨著不同氨氣濃度，而快速地反應電流變化，並在移除氨氣後能在短時間內回復到初始值。新穎的多孔有機薄膜電晶體具有相當的潛力應用在非侵入性、低成本的生物感測上，且感測極限能達到0.5ppm的氨氣濃度。

Organic thin-film transistors (OTFTs) have been extensively explored due to their potentials for low-end electronic applications: drivers for flexible displays, complementary circuits, and radio-frequency identficationtags(RFID). In this study, the electrical characteristics of pentacene-based thin film transistors with PVP or PVP-PMMA as gate dielectric were discussed. PVP is usually used as gate dielectric due to its low leakage current and high mobility. However, device with PVP gate dielectric exhibits obvious the bias stress effect and hysteresis to cause reliability issues. Compared with PVP device, there are slight bias stress effect and non hysteresis observed in the PVP-PMMA device. This difference between both devices may be influenced by the ambient environment. In the further experiment, devices were encapsulated in the dry environment. Compared with PVP-PMMA device, severe lower in the field-effect mobility of PVP device was observed. However, the bias stress effect and hysteresis are effective suppressed in both devices even for PVP-PMMA device after applying a 10000-sec bias and voltage is -30 V to the gate electrode. Based on the above results, the moisture absorption of OH groups in PVP dominates the hysteresis and the electron carrier capture. However, the hydrophobic of CH3 groups in PVP-PMMA block the moisture penetration to avoid the device degradation. In order to further study the moisture effect, the novel structure of PVP device was fabricated to accelerate the moisture penetration rate. When measurement was performed in the ambient air, high mobility and large drain current of the novel device were obtained. When measuring the device in N2 environment, mobility and drain current of the device become small. It is demonstrated that the polarized ratio of OH groups in the gate dielectric influences the carrier concentration in the channel. Based on this mechanism, the novel NH3 sensor is developed. This sensor was operated in the N2 environment while OH groups in PVP kept neutral. Following the entrance of NH3 gas, OH groups react with NH3 molecule to obtain electrons and these additional electrons induced extra hole carrier. The device drain current variation depends on different NH3 concentration and the response of current variation is fast. When removing NH3 gas, the drain current can quickly return to the original current. The novel porous OTFTs can be used as low-cost, non-invasive bio-sensing and its sensitivity can achieve 0.5-ppm ammonia.