Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO₂/ZrO₂ Superlattice Structure

Abstract

In contrast to traditional ferroelectrics such as perovskite Pb(Zr,Ti)O 3 , SrBi 2 Ta 2 O 9 , and organic polyvinylidene fluoride polymers, a special wake-up phenomenon has been widely observed in hafnia-based ferroelectric capacitors, which implies that the switchable polarization is subject to variation during the initial period of capacitor lifetime. [13] Although the spontaneous polarization is actually being enhanced during wake-up, [14] the variable device parameter can cause severe problems in applications. It has been reported that the crystallization temperature is highly relevant to the wakeup process. [13,[15][16][17] In particular, a high crystallization temperature could effectively render wake-up-free ferroelectric capacitors based on HZO. [17] Therefore, raising the processing temperature is a potential solution to get rid of the wake-up phenomenon.Nevertheless, using high crystallization temperature leads to other serious problems. On the one hand, hafnia-ferroelectric capacitors usually involve TiN or TaN electrodes, which are oxygen scavenger materials at high temperature. [18] On the other hand, high temperature crystallization tends to generate the thermodynamically stable monoclinic P2 1 /c phase (m-phase) for HfO 2 or HZO, which is paraelectric. [16,19] The robust stability of monoclinic phase hinders its transformation into the ferroelectric orthorhombic Pca2 1 phase (o-phase). Hence, in most published works, the crystallization temperature was controlled at around 500 °C. [17,20,21] In this work, we attempt a special design for the ferroelectric layer that can avoid the above two problems, thus permitting a higher crystallization temperature. First of all, the concept of HfO 2 /ZrO 2 superlattice enables crystallization from the ZrO 2 side. This is possible when ZrO 2 is adjacent to an inert electrode and the heat source is only from that electrode side during rapid thermal annealing (RTA). Standard RTA instruments typically possess heating modes from upper lamps, lower lamps and both. As is well-known, the m-phase of ZrO 2 can be less stable than its tetragonal phase due to surface energy consideration, as long as the grain dimension is sufficiently small. [22][23][24] Hence, even high temperature RTA may not transform nanoscale ZrO 2 into m-phase. Secondly, an inert electrode like Pt can be selected in conjunction with the ZrO 2 layer that isThe wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at a higher temperature has been reported to be effective in eliminating wakeup, but high temperature may yield the monoclinic phase or generate more oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of Hf 0.5 Zr 0.5 O 2 (HZO) superlattice ferroelectrics, which involves heating from the Pt/ZrO 2 interface side. It is demonstrated that 600 °C annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up...

HfO2–ZrO2 Ferroelectric Capacitors with Superlattice Structure: Improving Fatigue Stability, Fatigue Recovery, and Switching Speed

“…In order to further explore the internal differences between SL and HZO FE films during the applied electric field cycling, we employed the method of FORC to numerically analyze and distribute the E C and the internal bias field ( E bias ) of the HZO and SL FE films at initial, wake-up, fatigue, and recovery states. − Figure a illustrates the test sequences used for FORC diagram measurements at different states of the FE capacitors. To induce wake-up, fatigue, and recovery states, all devices were successively subjected to 10 3 cycles of square pulses with 3 V amplitude at 10 kHz, 10 7 cycles of square pulses with 2 V amplitude at 1 MHz, and 10 2 cycles of square pulses with 3 V amplitude at 10 kHz.…”

Effect of electrical stress on time dependent dielectric breakdown (TDDB) tolerate capability of HfO2–ZrO2 ferroelectric films with different thicknesses

“…To further investigate this point, the changes of E bias resulting from CVS was measured using the method of FORC [25][26][27][28] to numerically analyze the distribution of E c and E bias for the HZO films with different t HZO before and after CVS [31]. The test sequence used in this work was illustrated in figure 3.…”

“…Therefore, in this work, we examined the influence of FE film thickness on the TDDB tolerate capability of HZO film. Both positive and negative electrical stresses were applied, and the internal bias field (E bias ) before and after electrical stress conditions were measured and analyzed using the First Order Reversal Curves (FORC) method [25][26][27][28]. Statistical analysis and field distribution were obtained for all the HZO devices, providing valuable insights into the relationship between film thickness and TDDB properties.…”

Improved Endurance of Ferroelectric Hf0.5Zr0.5O2 Using Laminated-Structure Interlayer

“…The vertical migration and accumulation distribution of the oxygen vacancies promoted the generation and development of conduction in the current path, as shown in Figure 7 a. In the HfO 2 and ZrO 2 layers, the distributions of the oxygen vacancies were different [ 39 ]. The formation of highly conductive filaments in HfO 2 was accompanied by phase decomposition into hexagonal metal phases, such as Hf and h-Hf 6 O [ 40 ].…”