Low Temperature Fabrication of Capacitance Materials with High Dielectric Constant for Application of Non-Volatile Memory

采用射频磁控溅射装置，在衬底上施加射频偏压，制备了钛酸钡薄膜。用粉末靶代替烧结靶，可以获得接近化学计量比的薄膜。在这种情况下，薄膜的沉积速率和结晶度较少依赖于靶材料。在沉积过程中对衬底施加偏压，虽然由于沉积表面上的反向溅射，沉积速率略有下降，但薄膜的结晶得到了增强。根据施加在衬底上的平均负偏压和/或溅射靶的射频功率，薄膜中Ba/Ti的原子比略大于化学计量比，采用粉末混合靶制备了钛酸钡薄膜作为介质层的电容器结构，沉积薄膜的化学计量比基本满足要求。在较低的衬底温度下，例如，甚至300 ℃，它被证实，薄膜的结晶进行和薄膜的介电常数增加的生长表面上的离子轰击，并在给定的负偏压的薄膜的介电常数饱和。然而，过量的离子能量可能会导致介电损耗的增加。此外，电滞回线测试表明，沉积的薄膜具有高介电常数和（110）取向，显示出铁电特性，显示出作为电存储介质材料的可能性，但目前还不充分。通过优化沉积工艺，沉积的薄膜可以同时具有高的介电常数和低的介电损耗。在不久的将来，我们应该努力研究如何通过提高等离子体中的电离比来提高轰击离子的数密度，降低轰击离子的能量。

Barium titanate thin films were deposited with rf magnetron sputtering apparatus with rf substrate bias system. Using powder target in place of sintering target, the composition of deposited thin films could be close to the stoichiometric one. In this case, the deposition rate and crystallinity of thin films were less dependent of target materials. To apply the bias on substrate during deposition, the crystallization of thin films was enhanced, although the deposition rate was slightly decreased due to counter sputtering on deposition surface. According to the average negative bias to be applied on substrate and/or the rf power of sputtering target, the Ba/Ti atomic ratio in films were a little larger than the stoichiometric composition.The capacitor structure of barium titanate film as dielectric layer was fabricated using the powder mixture target, by which the stoichiometry of deposited films was almost satisfied. At low substrate temperature, for example, even 300 degree C, it was confirmed that the crystallization of films proceeded and the dielectric constant of films increased by ion bombardment on growth surface, and that the dielectric constant of films saturated over the given negative bias. However, the excess energy of ion might cause the increase of dielectric loss. In addition, the deposited thin film, which had the high dielectric constant and the (110) orientation, shows the ferroelectric characteristic by the measurement of hysteresis loop.The obtained films could show the possibility of dielectric material for the electric memory, although they were insufficient at this stage. By the optimization of the deposition process, the deposited films could have both high dielectric constant and low dielectric loss. In the near future, we should try to conduct hard research to increase the number density and decrease the energy of bombarded ion by the enhancement of ionization ratio in plasma.