Yoko Takada

Effect of Al-doped ZnO or Sn-doped In2O3 electrode on ferroelectric properties of (Pb,La)(Zr,Ti)O3 capacitors

Using chemical solution deposition, we fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors with either Al-doped ZnO (AZO) or Sn-doped In2O3 (ITO) top electrodes. Then, the effects of a thin conductive AZO or ITO buffer layer between the Pt bottom electrode and PLZT thin film were investigated in combination with an AZO or ITO top electrode (AZO/PLZT/AZO/Pt and ITO/PLZT/ITO/Pt). The H2 degradation resistance of the AZO/PLZT/AZO/Pt and ITO/PLZT/ITO/Pt capacitors was improved. For AZO/PLZT/AZO/Pt capacitors with 10- and 20-nm-thick buffer layers, the H2 degradation resistance was 91 and 81%, respectively, compared with 42–70% without a buffer layer. The H2 degradation resistance of ITO/PLZT/ITO/Pt capacitors with a 28-nm-thick buffer layer was improved to 85% from 60–76% without a buffer layer. The time-of-flight secondary ion mass spectrometry depth profile indicated that AZO is the better H2 barrier after forming gas (3% H2/balance N2) annealing.

Effect of excess Pb on ferroelectric characteristics of conductive Al-doped ZnO and Sn-doped In2O3 top electrodes in PbLaZrTiOx capacitors

Abstract The Pb content effect of chemical solution deposited lanthanum-doped lead zirconate titanate (PLZT) (Pb:La:Zr:Ti = Pb:3:30:70, Pb = 105∼117) was studied for conductive aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) deposited as top electrodes by means of pulsed laser deposition. The crystallinity, surface morphology, ferroelectric properties and hydrogen degradation resistance of the ITO/PLZT/Pt and AZO/PLZT/Pt capacitors were evaluated. All the PLZT films showed perovskite phase (revealed by X-ray diffraction patterns) and showed similar surface morphology and grain size (revealed by scanning electron microscopy images). PLZT capacitors with a Pb content of 113 exhibited the largest remnant polarization (at 15 V (300 kV cm−1)), however, the difference in hydrogen degradation resistance was small between the four levels of Pb content.

Comparative Study of Hydrogen- and Deuterium-Induced Degradation of Ferroelectric (Pb,La)(Zr,Ti)O 3 Capacitors Using Time-of-Flight Secondary Ion Measurement

Ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors were fabricated with Pt, Al:ZnO (AZO), or Sn:In2O3 (ITO) top electrodes. Hydrogen or deuterium-induced degradation was investigated for the three capacitors by annealing in a 3% H2/balance N2 or 3% D2/balance N2 ambient environment at 200 °C and 1 torr. The remnant polarization of all capacitors decreased after annealing in both H2 and D2 ambient after 45 min, and the remnant polarization of the Pt/PLZT/Pt capacitor significantly decreased after 45-min annealing compared with that of the AZO/PLZT/Pt and ITO/PLZT/Pt capacitors, even though the initial remnant polarization for the Pt/PLZT/Pt capacitor was larger. Time-of-flight secondary ion mass spectrometry showed slight differences in hydrogen content for the three different capacitors after H2 annealing. In contrast, the deuterium content of the Pt/PLZT/Pt and AZO/PLZT/Pt or ITO/PLZT/PT capacitors was significantly different after deuterium annealing. Deuterium depth profiles for the Pt/PLZT/Pt capacitor after annealing showed that deuterium conformally exists in the PLZT layer of the Pt/PLZT/Pt capacitor, and deuterium accumulation under the Pt bottom electrode was also observed. This result suggests that diffusion of deuterium in Pt was much higher than that in PLZT. AZO and ITO top electrodes could act as a hydrogen barrier layer for ferroelectric films.

Hydrogen profile measurement of (Pb,La)(Zr,Ti)O 3 capacitor with conductive electrode after hydrogen annealing

We fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors with Pt, Al:ZnO, or Sn:In2O3 top electrodes. The remnant polarization decreased for these PLZT capacitors after forming gas (3%H2/balance N2) annealing at 200°C and 1 Torr, especially for PLZT capacitor with Pt top electrodes due to the catalytic effect of Pt. The time-of-flight secondary ion mass spectrometry depth profile showed that the hydrogen content in PLZT thin films with Pt top electrode increased ca. 2.7 times after forming gas annealing compared with ca. 1.2 times with other electrodes.

Fabrication and electrical properties of a (Pb,La)(Zr,Ti)O3 capacitor with pulsed laser deposited Sn-doped In2O3 bottom electrode on Al2O3(0001)

A Sn-doped In2O3 (ITO) electrode was deposited on Al2O3(0001) using pulsed laser deposition at different oxygen pressures to create the bottom electrode of a (Pb,La)(Zr,Ti)O3 (PLZT) capacitor. The crystallographic orientation of the ITO films was controlled via the oxygen pressure. At 600 °C the (111) peak became dominant when the O2 pressure was increased, and when the pressure reached 2.0 Pa the ITO films became preferentially (111) oriented. The remnant polarization was 58.8–90.7 and 46.0–47.5 µC/cm2 for the Pt/PLZT/ITO and ITO/PLZT/ITO capacitors, respectively; the ferroelectric properties of these capacitors were also determined.

Comparative study of ferroelectric (K,Na)NbO 3 thin films pulsed laser deposition on platinum substrates with different orientation

We fabricated ferroelectric (K,Na)NbO₃ (KNN) capacitors on Pt(111) or Pt(100) bottom electrodes with different substrate temperature by pulsed laser deposition. The annealing effect in O₂ was also investigated. KNN film on Pt(100) substrate exhibited crystal grain clearly than that on Pt(111). The 2P_r and 2V_c, measured by ferroelectric tester, of Pt/KNN/Pt(111) for 400°C and 600°C were 4.28 and 4.58 μC/cm² and 1.21 and 0.469 V, respectively at applied voltage of 1 V. The 2P_r and 2V_c of Pt/KNN/Pt(100) capacitors for 710°C were 27.7 μC/cm² and 4.05 V at applied voltage of 5 V, respectively.

Evaluatioion of deuterium ion profile in (Pb,La)(Zr,Ti)O 3 capacitors structures with conductive oxide top electrode by time of flight secondary ion mass spectrometry

La-doped lead zirconate titanate (Pb,La)(Zr,Ti)O3 (PLZT) films were prepared via chemical solution deposition. Then, Pt, Al-doped ZnO (AZO), or Sn-doped In2O3 (ITO) top electrodes were deposited on the PLZT films to investigate ferroelectric properties. Three kinds of ferroelectric capacitors were annealed in 3% D2 (with N2 as a balance gas) to compare hydrogen-induced degradation of ferroelectric properties. Deuterium ion in ferroelectric capacitor was evaluated by time of flight secondary ion mass spectrometry. For ferroelectric capacitor with Pt top electrode, deuterium ion was detected in PLZT films after 5 min D2 annealing. On the other hands, deuterium ion was slightly detected with AZO and was not detected at all with ITO even after 120 min D2 annealing.

Ferroelectric properties of (Pb,La)(Zr,Ti)O3 capacitors employing Al-doped ZnO top electrodes prepared by pulsed laser deposition under different oxygen pressures

Al-doped ZnO (AZO) top electrodes were deposited under oxygen pressures from 0.02 to 20 Pa using pulsed laser deposition (PLD) to fabricate ferroelectric (Pb,La)(Zr,Ti)O3 capacitors. The oxygen pressure during PLD affected the surface morphology of the AZO top electrodes as well as the ferroelectric properties. In particular, the surface morphologies were dramatically altered by increasing oxygen pressure. We obtained desirable ferroelectric properties with the highest maximum polarization and lowest coercive voltage at around 2.0 Pa. The saturation characteristics, hydrogen degradation resistance, and fatigue resistance were almost unrelated to the oxygen pressure during PLD.

The orientation controlled (Pb,La)(Zr,Ti)O 3 capacitor for improved reliabilities

We fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors by pulsed laser deposition (PLD) and investigated the effects of substrate temperature during PLD, Pb contents of the target, annealing temperature and period to improve ferroelectric properties. The R.T. deposition with higher Pb contents in the target (1.27) and subsequent annealing at 750°C for 10 min exhibited the best ferroelectric properties in this work. With higher deposition temperature than R.T. and lower annealing temperature than 700°C, large hysteresis loops were not observed.

Comparative study of electrical properties of PbLaZrTiOx capacitors with Al-doped ZnO and ITO top electrodes

PbLaZrTiOx (PLZT) thin films were deposited on Pt(111) substrate by the sol-gel method, then aluminum-doped zinc oxide (AZO) and indium tin oxide (ITO) top electrodes were deposited by pulsed laser deposition (PLD). We evaluated degradation characteristics by 3% hydrogen atmosphere annealing in 200°C, 1Torr. The polarization ratio of PLZT capacitors with 200 nm top electrodes thickness was maximum value at the same Pb contents. We also evaluated fatigue behavior by applying 10 V, 100 μs pulse width and 1 ms interval cycles. PLZT capacitors with AZO and ITO top electrodes were robust electrodes over 105 cycles compared with Pt top electrodes.