Tomoyuki Sakoda

Hydrogen-Robust Submicron IrOx/Pb(Zr, Ti)O3/Ir Capacitors for Embedded Ferroelectric Memory

We have demonstrated that the scaling of IrOx (Pb(Zr, Ti)O3:PZT)/Ir capacitors can be extended into the submicron regime. The submicron IrOx /PZT/Ir capacitors were fabricated using a one-mask stack-etch process, integrated with an SiO 2 interlayer dielectric, and contacted with Al metallization. The aggregate electrical properties of integrated PZT capacitor arrays are shown to be nearly independent of individual capacitor area in the range between 10 2 µm 2 and 0.12µm 2 . In particular, switched polarization values of more than 30µC/cm 2 were obtained for PZT capacitors with an individual capacitor area of 0.12 µm 2 . This result suggests that the lateral scaling can be achieved down to 0.1 µm 2 . Through the use of appropriate diffusion barriers, hydrogen-robust submicron PZT capacitors are obtained. No degradation in ferroelectric properties of submicron PZT capacitors was observed under the test conditions. These results suggest that PZT capacitors can be integrated into a standard complementary metal oxide semiconductor (CMOS) process flow with minimal degradation.

Effects of post-oxidation annealing on 3nm-thick low-temperature-grown gate oxide

Abstract The reduction of the oxidation temperature is effective for atomically-controlled gate oxide growth. We focus the effects of post-oxidation annealing on oxides grown at a low temperature from 650 to 850°C. The N 2 annealing drastically decreased the leakage current at the low gate voltage below 1.5 V. The interface trap density was also reduced by the N 2 annealing. We confirmed the correlation between the interface trap density and the leakage current at a low voltage below 1.5 V. We also found that the stressing immunity of the ultrathin oxides grown at a low temperature, 650°C, is dramatically improved by post-oxidation annealing at 850°C.

Characterization of Switching Properties of Lead-Zirconate-Titanate Thin Films in Ti-Rich Phase

Switching behaviors of lead-zirconate-titanate thin-film capacitors with Ti/Zr ratios of 60/40 and 75/25 were successfully characterized by observing their switching transient currents. The capacitor with 60/40 showed the remanent polarization density of 24.0 µ/cm2 independent of the frequency of the external switching biases. On the other hand, the remanent polarization density of the capacitor with 75/25 was reduced markedly with increasing the frequency. The remanent polarization density was lowered from 23.6 µC/cm2 at 100 Hz to 13.0 µC/cm2 at 12.5 kHz. While the switching transient currents were observed as a function of time, the lead-zirconate-titanate thin-film capacitor with 60/40 showed the typical sharp switching transient current. In sharp contrast, the capacitor with 75/25 ratio showed a monotonous transient current which suggests the presence of ferroelectric domains having long time constants. Consequently, the lead-zirconate-titanate thin film with the Ti/Zr ratio of 60/40 showed better switching behavior as compared to that with the Ti/Zr ratio of 75/25.

Characterization of Sputtered Lead-Zirconate-Titanate Thin Films with Various Compositions

Sputtered Pb(Zr,Ti)O3 (PZT) thin films with various compositions were characterized. Comparing sputtered PZT films with sol-gel PZT films, it was found that the film composition can be approximately estimated from the distance of the PZT (100) lattice plane. The sputtered PZT thin films with a Ti-rich phase showed excellent ferroelectric properties. The remanent polarization density, the coercive field and the saturation voltage of 300-nm-thick PZT capacitors with Zr/Ti=35/65 were 42 µC/cm2, 46 kV/cm and 3.2 V, respectively. Those of 300-nm-thick PZT capacitors with Zr/Ti=30/70 were 42 µC/cm2, 48 kV/cm and 2.5 V, respectively. The polarization retention properties of PZT capacitors with a Ti-rich phase are outstanding, and the value of the retained polarization density after 10 years is expected to be larger than 40 µC/cm2.

Interfacial Layer in Thermally-grown Ultra thin Silicon Dioxides Measured by Grazing Incidence X-Ray Reflection

The effects of oxidation temperature and post-oxidation annealing (POA) on density variation within ultra-thin (3 nm) silicon dioxide films were investigated via grazing incidence X-ray reflection (GIXR). At the SiO2/Si interface, it was found that the oxide films without POA have slightly denser layers than those of the bulk. These interfacial layers were found to be thicker for the oxide grown at a lower temperature and to become indistinguishable from the bulk of the film after POA.

Control of Grain Structure of Sputtering Lead-Zirconate-Titanate Thin Film Using Amorphous Lead-Titanate Buffer Layer

Crystalline lead-zirconate-titanate (PZT) films of perovskite structure with fine grains were successfully obtained on Ir substrates using an amorphous lead-titanate (a-PTO) buffer layer. The grain size of PZT ranged from 100 to 150 nm. The results of the temperature dependence of the X-ray diffraction patterns of PZT films prepared on a-PTO buffer layer revealed that PZT films with a single perovskite phase were obtained at 500°C. In addition, 250-nm-thick PZT films fabricated with a-PTO buffer layer and crystallized at 600°C showed excellent ferroelectric properties. The 2Pr values of Ir/PZT/Ir capacitors with a-PTO buffer layer satisfactorily saturated at the applied voltage of 3.5 V. No degradation in the polarization density was observed for switching cycles up to 1×109.

Recovery of the Ferroelectric Properties of Hydrogen-Damaged Ir/Pb(Zr,Ti)O3/Ir Capacitors by Post Annealing

In this paper, the recovery of the ferroelectric properties of Ir/Pb(Zr,Ti)O3/Ir thin film capacitors damaged by annealing in a hydrogen ambient has been described. The ferroelectric properties of the capacitors markedly degrade as a result of heat treatment in a hydrogen ambient at 400°C. These properties can be easily recovered to their initial state by post annealing using a rapid thermal annealing process in an oxygen ambient at 400°C for 1 min.

Recent progress in sputtering PZT thin films for ferroelectric memories

Abstract This paper describes amorphous Pb(Zr, Ti)O3 (PZT) thin films deposited by cosputtering Pb(Zr0.5 Ti0.5)O3 and PbO targets. By optimizing the amount of the excess Pb and the deposition temperature, PZT thin films with a single perovskite phase were obtained successfully on Ir substrates and Pt substrates at 520°C. 250-nm-thick PZT films crystallized by rapid thermal annealing (RTA) at 600°C for 20 s exhibited excellent ferroelectric properties: a coercive voltage of 1.0 V, a remanent polarization density of about 40 μC/cm2, and a polarization switching endurance over 1x109 cycles. Although a heat treatment in a reductive ambient causes degradation of ferroelectric properties of PZT thin films, their degraded ferroelectric properties can be easily recovered from by a 1-min RTA in an oxygen at 400°C.

Sputtered Pb(Zr, Ti)O 3 Thin Films for Ferroelectric Capacitors

Sputtered Pb(Zr, Ti)O 3 thin films with superior ferroelectric properties were successfully obtained by controlling the grain structure and the film compositions. We found that amorphous PbTiO 3 buffer layers are effective in forming PZT thin films with fine dense grains. The sputtered PZT thin films with Ti-rich phase showed excellent ferroelectric properties. The polarization retention properties of PZT capacitors with Ti-rich phase are remarkable, and the value of the retained polarization density after 10 years is expected to be larger than 40 μC/cm 2 . Further, 150-nm-thick PZT capacitors with Zr/Ti=30/70 showed 2 P , at 1.5 V of more than 30 μC/cm 2 , and good retention property. These results indicate the potential of the lower voltage operation of sputtered PZT capacitors by optimizing the film composition and thickness.