Method for disclosing invisible physical properties in metal−ferroelectric−insulator−semiconductor gate stacks. (28th March 2017)

• Record Type: Journal Article
• Authors: Sakai, Shigeki; Zhang, Wei; Takahashi, Mitsue
• Is Part Of: Journal of physics. Volume 50:Number 16(2017)
• Publication Date: 2017-03-28
• Subjects: FeFET -- nonvolatile memory -- ferroelectricity -- device physics; Physics -- Periodicals; 530
• DOI: 10.1088/1361-6463/aa622f
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: In metal–ferroelectric–insulator–semiconductor gate stacks of ferroelectric-gate field effect transistors (FeFETs), it is impossible to directly obtain curves of polarization versus electric field ( P f − E f ) in the ferroelectric layer. The P f − E f behavior is not simple, i.e. the P f − E f curves are hysteretic and nonlinear, and the hysteresis curve width depends on the electric field scan amplitude. Unless the P f − E f relation is known, the field E f strength cannot be solved when the voltage is applied between the gate meal and the semiconductor substrate, and thus P f − E f cannot be obtained after all. In this paper, the method for disclosing the relationships among the polarization peak-to-peak amplitude (2 P mm_av ), the electric field peak-to-peak amplitude (2 E mm_av ), and the memory window ( E w ) in units of the electric field is presented. To get P mm_av versus E mm_av, FeFETs with different ferroelectric-layer thicknesses should be prepared. Knowing such essential physical parameters is helpful and in many cases enough to quantitatively understand the behavior of FeFETs. The method is applied to three groups. The first one consists of SrBi2 Ta2 O9 -based FeFETs. The second and third ones consist of Ca x Sr1− x Bi2 Ta2 O9 -based FeFETs made by two kinds of annealing. The method can clearly differentiate the characters of the three groups. By applying the method, ferroelectric relationships among P mm_av, E mm_av, and E w are well classified in the three groups according to the difference of the material kinds and the annealing conditions. The method also evaluates equivalent oxide thickness (EOT) of a dual layer of a deposited high- k insulator and a thermally-grown SiO2 -like interfacial layer (IL). The IL thickness calculated by the method is consistent with cross-sectional image of the FeFETs observed by a transmission electron microscope. The method successfully discloses individual characteristics of the ferroelectric and the insulator layers hidden in the gate stack of a FeFET.