The Ferroelectric and Charge Injection Effects of Metal–Ferroelectric (BiFe[sub 0.95]Mn[sub 0.05]O[sub 3])–Insulator (Bi[sub 2]Ti[sub 2]O[sub 7])–Silicon Capacitors

Abstract

Metal-ferroelectric-insulator-silicon capacitors with a BiFe 0.95 Mn 0.05 O 3 ͑BFMO͒ ferroelectric film and a Bi 2 Ti 2 O 7 ͑BTO͒ insulator have been fabricated. The electrical properties of 300 nm thick BFMO were investigated for different BTO thicknesses. The experimental results show that BFMO/BTO ͑50 nm͒ exhibits the largest maximum memory window. Furthermore, the trapped and mobile positive charges initiate at Ϯ7 and Ϯ8 V, respectively. Compared with BFMO/BTO ͑30 nm͒ and BFMO/BTO ͑70 nm͒, the BFMO/BTO ͑50 nm͒ shows a relatively long retention time.The ferroelectric field-effect transistor with a metalferroelectric-insulator-silicon ͑MFIS͒ structure has emerged as promising nonvolatile memory with nondestructive readout capability. 1 The insertion of the insulator is purposed to prevent the interdiffusion and reaction between the ferroelectric film and Si substrate. Moreover, a proportionally larger voltage is expected to be applied across the ferroelectric film. 2 As in lead zirconate titanate ͑PZT͒ ͑290 nm͒/Y 2 O 3 ͑11.8 nm͒/Si, the distribution of the applied voltage for PZT is as large as 5.22 V at 8 V. 3 For PZT ͑230 nm͒/Dy 2 O 3 ͑20 nm͒, the ratio of the voltage drop across the ferroelectric and insulator is only 1:3. 4 The voltage across the ferroelectric layer in PZT ͑160 nm͒/La 2 O 3 ͑16 nm͒ is also one-fourth of the total applied voltage. 5 These researches show that selecting a high-k and thinner insulating layer is necessary to guarantee a larger electric field across the ferroelectric layer.Because of that, the BiFeO 3 -based films have a low crystallization temperature, a large coercive voltage, and a small dielectric constant; the BiFeO 3 -based MFIS structures have begun to be studied. 6-8 However, the effect of the insulator thickness on memory properties of the MFIS capacitor has rarely been reported. In addition, compared with other ferroelectric films, such as PZT, ͑Bi,La͒ 4 Ti 3 O 12 , and SrBi 2 Ta 2 O 9 , the BiFeO 3 -based film has a larger coercive field, which needs a larger distributed voltage across the ferroelectric film to ensure polarization switching. Therefore, to operate at a low voltage with a saturated electric field applied to the BiFeO 3 -based film, optimization of the buffer layer capacitance is important in MFIS configurations. 4 The Bi 2 Ti 2 O 7 ͑BTO͒ film has a high dielectric constant and a low leakage current density. 8 It has been successfully used as an effective diffusion barrier between the ferroelectric film and the Si substrate. 9,10 In this work, the electrical properties of BiFe 0.95 Mn 0.05 O 3 ͑BFMO͒ ferroelectric film deposited on the BTO insulator of various thicknesses are investigated. The results demonstrate that the Au/BFMO ͑300 nm͒/BTO ͑50 nm͒/Si shows relatively better memory characteristics than the reported BiFeO 3 -based MFIS structures. ExperimentalDifferent from the previous synthesis of the BTO buffer layer, 11 we modified the preparation process. Bismuth nitrate Bi͑NO 3 ͒ 3 ·5H 2 O and titanium isopropoxide Ti͓OCH͑CH 3 ͒ 2 ͔ 4 were selecte...