Evaluation of polarization characteristics in metal/ferroelectric/semiconductor capacitors and ferroelectric field-effect transistors

Abstract

In this study, we propose a measurement technique for evaluating ferroelectric polarization characteristics in ferroelectric field-effect transistors (FeFETs). Different from standard metal/ferroelectric/metal capacitors, the depletion and inversion phenomena in semiconductor substrates have to be carefully taken into account when evaluating the ferroelectric properties using fast voltage sweep as input. The non-equilibrium deep depletion is found to be the limiting factor for the accurate evaluation of ferroelectric properties in metal/ferroelectric/semiconductor capacitors. By connecting the source, drain, and substrate of the FeFET together during the polarization measurement, the deep depletion can be suppressed and the ferroelectricity of the ferroelectric gate can be accurately evaluated. The present technique is a powerful method for capturing the polarization states in FeFETs, enabling new approaches for device characterization and fundamental study, and overcomes the limitation found in the conventional polarization measurement on 2-terminal metal/ferroelectric/semiconductor capacitors.Ferroelectric field-effect transistors (FeFETs), in which ferroelectric thin films are employed as FET gate insulators, are promising for non-volatile memory devices 1-3 and synaptic devices in computing-in-memory applications. 4-6 A substantially increasing interest in FeFETs can be seen after the discovery of ferroelectric HfO 2 7 thanks to its scalability and CMOS compatibility, 3 with FeFETs having excellent performance being continuously reported. [8][9][10][11] So far, the characterization of FeFETs is mainly limited to the standard evaluation of I d -V g characteristics and threshold voltage shift ∆V T as well as their retention and endurance properties. 3,5,[8][9][10][11][12][13][14][15][16][17] On the other hand, the ferroelectric properties of the ferroelectric gate insulators are usually evaluated in an indirect manner, by preparing separate metal/ferroelectric/metal (MFM) capacitors for characterization. 3,5,8,[14][15][16] It is usually assumed that the ferroelectric properties of the separately-prepared MFM capacitors can well reproduce those of the ferroelectric gate insulators in the FeFETs. However, it is questionable whether MFM capacitors can represent the ferroelectricity of the ferroelectric gate insulators, particularly for metal/ferroelectric/semiconductor (MFS, or sometimes called MFIS if the dielectric insulator layer should be emphasized)-type FeFETs, as it is well recognized that the ferroelectric properties of HfO2 is strongly dependent on the underlying and capping layers. [17][18][19][20] To carry out more accurate characterization, MFS capacitors are frequently employed to reproduce the same substrate condition as the ferroelectric gates in FeFETs. 17,21,22 By characterizing MFS capacitors, it has been reported that semiconductor substrates have a significant effect on the ferroelectric properties. 23,24 On the other hand, there are two concerns with the characterization of separate MFS capaci...

Low‐Thermal‐Budget Fluorite‐Structure Ferroelectrics for Future Electronic Device Applications

“…Numerous studies conducted in several research groups in the last decade have demonstrated that fluorite‐structure ferroelectrics can be deposited using various deposition techniques such as ALD, sputtering, pulsed laser deposition (PLD), chemical vapor deposition (CVD), and chemical solution deposition (CSD). [ 1–19,22–54 ] Among these techniques, ALD was the most intensively studied deposition technique because it can form very thin conformal and uniform ferroelectric films based on a self‐limiting mechanism by chemical reactions between metal precursors, oxygen source, and the previously deposited film (or substrate). In this regard, the only controllable parameters during the ALD process are types of metal precursor/oxygen sources, [ 27–29 ] pulse/purge time, [ 30,31 ] and deposition temperature.…”

“…Depending on the type of material, the formation of the ferroelectric phase during the annealing process (or partially during the ALD process) can be enhanced by controlling the applied stress due to the difference in the thermal expansion coefficient or increasing the concentration of oxygen vacancies at the interface by the oxygenscavenging effect. [2,4,5,[47][48][49][50][51][52] In this regard, the influence of various bottom electrodes on ferroelectric properties has been extensively studied based on the metal-ferroelectric-metal (MFM) structure. [47][48][49][50][51] According to the experimental results reported in the past decade, the use of TiN bottom electrodes could be a useful strategy to improve the ferroelectric properties of Hf 1-x B x O 2 films.…”

“…[2,4,5,[47][48][49][50][51][52] In this regard, the influence of various bottom electrodes on ferroelectric properties has been extensively studied based on the metal-ferroelectric-metal (MFM) structure. [47][48][49][50][51] According to the experimental results reported in the past decade, the use of TiN bottom electrodes could be a useful strategy to improve the ferroelectric properties of Hf 1-x B x O 2 films. [2,4,47] Moreover, it was found that ferroelectric properties, especially endurance, can be further improved by the deposition method of the TiN bottom electrode: >10 10 cycles in ALD TiN and %10 9 cycles in sputtered TiN at a pulse amplitude of 2.5 MV cm À1 .…”

Trench FinFET Nanostructure with Advanced Ferroelectric Nanomaterial HfZrO2 for Sub-60-mV/Decade Subthreshold Slope for Low Power Application

“…To prove the ferroelectric behavior of the 5-nm-thick ferroelectric layer, grazing incident X-ray diffraction (GIXRD) (PANalytical, Malvern, United Kingdom) and positiveup-negative-down (PUND) measurement were performed. Figure 4a presents the GIXRD analysis of the 5-nm-thick HZO film annealed at 500 • C for 30 s. The GIXRD pattern of ALD HZO showed strong peaks at approximately 30 • and 35 • that corresponded to the ferroelectric orthorhombic phase with space group Pbc2 1 [20]. Figure 4b presents the polarizationvoltage (P-V) curve measured by the PUND method for the metal/ferroelectric/insulator/ semiconductor (MFIS) capacitor with 5 nm HZO after RTA at 500 • C for 30 s, which was the same condition as used for the fabricated devices.…”

Reliability of HfO2-Based Ferroelectric FETs: A Critical Review of Current and Future Challenges

“…In FeCAPs, P-V loops are mostly derived indirectly through monitoring of the current through the stack when applying triangular-shaped voltage inputs. Conversely, in FeFETs characterization of the P-V loop differs from that of MFM stacks (even for the same ferroelectric material and thickness) because of incomplete charge screening and influence of underlying and capping layers on the FE-HfO2 [164]. In fact, relatively low doping of the semiconductor body in FeFETs can cause the deep-depletion effect, that impedes the formation of the inversion layer required to screen the polarization charge and thus to correctly characterize the P-V loop [164].…”