鈦酸鍶鋇薄膜之溫度電特性探討

Abstract

鐵電材料由於具有高介電常數以及壓電性，熱電性等特點，近來廣泛應用在動態隨機存取記憶體的電容器以及各種感測元件上面。 一般來說，鐵電材料具有兩種狀態：順電相與鐵電相。當溫度高於居禮溫度時，呈現順電相，反之，則呈現鐵電相。動態隨機存取記憶體便是利用在順電相時具有高介電常數的特點，而溫度感測器則是利用在相變時，介電常數或電阻發生巨大變化，偵測電容或電流變化以得知溫度的變化。因此，我們可以知道，溫度對於鐵電材料的電性影響是很大的，所以本論文著重在溫度對於鈦酸鍶鋇薄膜電性上的影響，特別是在電流機制以及溫度電阻效應方面。 首先，我們將鈦酸鍶鋇薄膜濺鍍在Pt/TiN/Ti/Ox的基板上面，接著濺鍍Pt為上電極，形成金屬/絕緣層/金屬(MIM)的結構，再經過不同溫度的快速熱退火處理之後，進行電性量測。我們改變量測時的基板溫度，以得知溫度對於鈦酸鍶鋇薄膜電性上的影響。 接下來，同樣在Pt/TiN/Ti/Ox的基板上，我們濺鍍了鈦酸鍶鋇/鉻/鈦酸鍶鋇(BST/Cr/BST)多層薄膜的結構，接著濺鍍Pt為上電極，在經過高溫長時間的爐管退火處理，利用熱擴散的方式，使鉻進入上下兩層的鈦酸鍶鋇薄膜之中，然後再進行電性量測。同樣地，我們改變量測時的基板溫度，以得知溫度對於添加鉻的鈦酸鍶鋇薄膜電性上的影響。 我們發現鈦酸鍶鋇薄膜具有不錯的正溫度電阻效應，並可以Heywang model來加以解釋；此外，當添加了鉻之後，有效地降低了鈦酸鍶鋇薄膜的漏電流，而且大幅提昇了正電阻效應，對於不管是在動態隨機存取記憶體或是熱敏電阻的運用上，都是很有利的。

Ferroelectric materials with high dielectric constant, pyroelectricity and piezoelectricity have recently been extensively applied on DRAM capacitors and sensors. For ferroelectric materials, when temperature is higher than Curie temperature (Tc), they are paraelectric, while they are ferroelectric if temperature is lower than Tc. For DRAM applications, paraelectric (Ba,Sr)TiO3 (BST) is applied because of its high dielectric constant. For applications on sensors, large variations of dielectric constant and resistivity of BST thin films with temperature during phase transition are used to improve sensitivity. Thus the temperature effects on the electrical properties are important, especially on conduction mechanism and temperature coefficient of resistivity (TCR) effect. The BST thin films with low crystallization temperature were deposited onto the Pt/TiN/Ti/Ox/Si substrate by rf magnetron sputter at 300oC substrate temperature. The BST thin films were then post annealed by rapid thermal annealing (RTA). Finally, physical and electrical properties of the BST thin films were investigated. In order to investigate the properties of the Cr-incorporated BST thin films, the BST/Cr/BST multi-films structure was deposited on Pt/TiN/Ti/Ox/Si substrate by rf magnetron sputter at 300oC substrate temperature. High temperature and long period furnance annealing was adopted as post treatment method to implement thermal diffusion of Cr into BST thin films. The effects of Cr incorporation were investigated by means of different annealing temperature, Cr film thickness, and measurement temperature. In our experiments, BST thin films revealed positive TCR (PTCR) effect. For Cr-incorporated BST films, advantages of leakage suppression and PTCR enhancement can be applied on DRAM capacitors and thermal sensors.