Pb5Ge3O11 Thin Films Research Articles

Preparation, Microstructure and Physical Characteristics of Ferroelectric Pb5Ge3O11 Thin Films for Memory Application

ABSTRACTWe report sol-gel process of Pb5Ge3O11 (PGO) as well as the microstructure and physical properties of ferroelectric PGO films for memory applications. The PGO sol was prepared from lead acetate hydrate, germanium isopropoxide, and di(ethylene glycol) ethyl ether. The reactions taking place during the sol-gel process were examined in detail. Diethanolamine (DEA) was added to help maintain the desired species ratio and prevent germanium oxide precipitation. The preferred orientation of the PGO thin films was well controlled by the heating and reflux procedures in the sol-gel preparation process. Additionally, to examine the impact of postdeposition processing, selected samples were oxygen annealed at temperatures ranging from 450–650°C. The samples were characterized with X-ray diffraction (XRD), non-contact (planview) atomic force microscopy (NC-AFM). The resulting data indicate that the microstructure and physical properties of PGO films depend strongly on the precursor preparation as well as the post deposition annealing temperature.

Ferroelectric Pb5Ge3O11 MFMOS capacitor for one transistor memory applications

The basic mechanism for an one transistor memory device has been studied. Many ferroelectric materials such PbZrxTi1−xO3 (PZT), SrBi2Ta2O9 (SBT), Pb5Ge3O11 (PGO) etc. were analyzed for this application. Because of its low remanent polarization and low dielectric constant, the c-oriented Pb5Ge3O11 thin film was selected for one-transistor memory applications. Pb5Ge3O11 thin films have been prepared using MOCVD and RTP (Rapid Thermal Process) post-annealing. Lead bis-tetramethylheptadione [Pb(thd)2] and germanium ethoxide [Ge(OC2H5)4] were used as the precursors. The Pb5Ge3O11thin films were deposited onto Ir/Ti/SiO2/Si wafers to measure their compositions, phase formation, microstructure and ferroelectric properties. The extremely highly c-oriented Pb5Ge3O11 thin films showed good ferroelectric and electrical properties. A 300 nm thick PGO thin film exhibited a square and saturated hysteresis loop with 2Pr of 3.98 μC/cm2, 2Ec of 128 KV/cm at an applied voltage 5V, leakage current of 5.1×10−7 A/cm2 at 100 KV/cm, and dielectric constant of close to 36. The c-axis oriented Pb5Ge3O11 thin film also exhibited very good retention properties. The experimental results showed that a Pb5Ge3O11 MFMOS gate stack is suitable for one-transistor memory applications.

Deposition and properties of spin on Pb5Ge3O11 ferroelectric thin film

This paper will discuss the spin on deposition of Pb5Ge3O11(PGO) on Ir and ZrO2 substrates for MFMIS and MFIS FeRAM applications. The precursors used are lead acetate trihydrate and germanium isopropoxide in di (ethylene glycol) ethyl ether. After optimizing the deposition conditions of spin speed, baking condition and annealing condition, single phase c-axis PGO has been obtained on both Ir and ZrO2 substrates. The film deposited on Ir substrate shows extremely smooth surface and very well saturated square shape hysteresis loop. The 2Pr is about 6∼8 μC/cm2, dielectric constant is about 50∼100, and the leakage current is about 3×10−6 A/cm2 at 100 kV/cm for 100–120nm thickness PGO thin film. The PGO thin film deposited on ZrO2 is also very uniform. About 0.7V memory window observed for 180nm PGO thin film with 13nm ZrO2 high-k gate dielectric at 2V sweep voltage. The leakage current is about 2.5×10−7 A/cm2 at 100 kV/cm

Preparation and characterization of lead germanate (pb5ge3o11) thin film by pulsed laser deposition

Lead germanate (Pb5Ge3O11) thin films with c-axis preferred orientation were prepared by pulsed laser deposition and RTA process and ferroelectric properties were obtained in the films. RBS composition analysis indicated that films were formed close to stoichiometric target composition at oxygen pressure below 2 mTorr during deposition. Films post-annealed at 550°C for 10 minutes showed symmetrical hysteresis loops with remanent polarization of about 1 μC/cm2 and coercive field of 92 kV/cm at an applied voltage 5 V. The leakage current density of films is about 6.5×10−7 A/cm2 at 100 kV/cm.

Integration Processes and Properties of Pt/Pb5Ge3O11/(Zr, Hf)O2/Si One Transistor Memory Devices

AbstractThe basic mechanism for one transistor memory device has been studied. Ferroelectric material, Pb5Ge3O11 (PGO) was selected for MFOS (M: Metal, F: Ferroelectrics, O: oxide, S: silicon) memory transistor fabrication. Processing of one-transistor memory devices dealt with the following issues: decomposition of ferroelectric materials, the etching damage of ferroelectric materials, the forming gas annealing damage of ferroelectric materials, the selective deposition of ferroelectric materials, the alignment for device making processes. The integration processes for one transistor memory device have been optimized to reduce process-induced damages. The gate dielectric material is (Zr, Hf)O2. Extremely high c-axis oriented Pb5Ge3O11 thin films were successfully deposited on high k gate oxide. Memory transistors having 0.6, 3 and 10μm channel length and 10 μm channel width have been fabricated. The memory windows are around 1 - 2V. The memory windows are almost saturated from operation voltage of 4V. After programming at -5V (on “off” state), the drain current (ID) at VD of 1V and VG of 2.5 V is about 1.15 ×10−10A. After programming at 5 V (on “on” state) the drain current (ID) at VD of 1V and VG of 2.5 V is measured about 6.4 ×10−8 A, which was 2.5 order higher than that of “off” state.

The properties of mfmos one transistor memory devices

Integration processes for one transistor memory device have been optimized to reduce process-induced damages. One-transistor ferroelectric memory devices with MOCVD Pb5Ge3O11 (PGO) MFMOS memory cells have been fabricated. The hysteresis loop of a 300 nm thick PGO thin film capacitor exhibited a square and saturated form with 2Pr of about 4 μC/cm2 and 2Ec of 134 KV/cm at an applied voltage of 5V. The capacitor leakage current is 1– 5 × 10−7 A/cm2 at 100KV/cm. The peak dielectric constant is around to 35 – 45. The c-axis oriented Pb5Ge3O11 thin film also showed very good retention properties. The 1T-memory devices showed memory windows around 2V. The memory windows were almost saturated when the operation voltage is 2V. After programming to -4 V (on “off'’ state), the drain current (Id) of the memory transistor operated at Vd of 0.1V and Vg of 0.5 V is about 1×10−8 A. After programming to 4V (on “on” state) the drain current (ID) of the device operated at VD of 0.1V and VG of 0.5 V is about 1 ×10−6 A, which is about 100 times high than that of “off state. The device also exhibits excellent imprint and fatigue properties.

Preparation and properties of PGO thin films by PLD

Lead germanate, Pb5Ge3O11 (PGO), is known to be ferroelectric with a large pyroelectric property and relatively small dielectric constant. In this paper, we investigated the optimal conditions for the c-axis oriented PGO thin films. The effectiveness of oxygen (O2) as an oxidizing agent during in-situ growth of PGO thin films on YBCO/LaAlO3(100) substrates is studied as a function of substrate temperature. Films with c-axis preferred orient can be obtained at a substrate temperature of 650°C for 20min with oxygen pressure 26.6 Pa followed by subsequent annealing temperature at 400 °C for 30min to keep good YBCO layers.

The ferroelectric properties of c-axis oriented Pb5Ge3O11 thin films prepared by metalorganic chemical vapor deposition

C-axis oriented ferroelectric Pb5Ge3O11 thin films were prepared on Pt/Ir-coated Si wafers by metalorganic chemical vapor deposition (MOCVD) and rapid thermal process annealing techniques. The films were specular and crack free and showed complete crystallization with c-axis orientation for growth temperatures between 500 and 550 °C. Good ferroelectric properties were obtained for a 150-nm-thick film with Pt/Ir electrodes: the remanent polarization (2Pr) and coercive field (2Ec) values were about 3.8 μC/cm2 and 93 kV/cm, respectively. The films also showed excellent fatigue characteristics: no fatigue was observed up to 1×109 switching cycles. The leakage current increased with increasing applied voltage, and is about 3.6×10−7 A/cm2 at 100 kV/cm. The dielectric constant showed behavior similar to most ferroelectric materials in that the dielectric constant changed with applied voltages. The maximum dielectric constant is about 45. High-quality MOCVD Pb5Ge3O11 films can be used for single transistor ferroelectric memory devices.

MFMOS Capacitor with Pb5Ge3O11 Thin Film for One Transistor Ferroelectric Memory Applications

AbstractA ferroelectric Pb5Ge3O11 thin film with a low dielectric constant is proposed for application in one transistor ferroelectric memories. A strong depolarization voltage on the ferroelectric capacitor with MIFSFET structures diminishes the remanent polarization significantly and, therefore, the low dielectric constant becomes very important to widen the memory window. A memory window of 3V was estimated for the MFMOS memory structure with 2000Å ferroelectric Pb5Ge3O11 and a 100Å gate oxide. In the second part of this paper, Pb5Ge3O11 films deposited on Ir/Ti/SiO2/Si substrates, by using MOCVD system, was demonstrated. Germanium ethoxide, Ge(OC2H5)4, and lead bis-tetramethylheptadione, Pb(thd)2, were used as the MOCVD precursors. The film composition, phase formation, microstructure and ferroelectric properties are reported. The c-axis oriented Pb5Ge3O11 thin films prepared by MOCVD and RTP post-annealing showed a square ferroelectric hysteresis loop with Pr of 2.83 μC/cm2 and EC of 49 kV/cm. A low leakage current of 7.5 × 10−7 A/cm2 at 100 kV/cm and low dielectric constant of 41 were also demonstrated.

MOCVD Process of Ferroelectric Lead Germanate Thin Films and Bottom Electrode Effects

AbstractPb5Ge3O11 is a new promising candidate for nonvolatile memory such as one-transistor memory applications because of its moderate polarization and relative low dielectric constant. But this material is a low symmetry ferroelectric material and it is said the spontaneous polarization exists only along the c-axis. Furthermore, in the PbO- GeO 2 system, the stability range for the Pb5Ge3O11 phase is very limited and that even a relatively small deviation in composition or in growth temperature could lead to the formation of other lead germanate compounds. Many methods have been used to grow Pb5Ge3O11 film. This is the first time the Pb5Ge3O1 thin film has been successfully grown by advanced MOCVD technique with a liquid delivery system. This paper will discuss the MOCVD process for growing Pb5Ge3O11 thin films on different electrodes (Pt, Ir and Pt/Ir). The properties of these electrodes, the microstructures of the Pb5Ge3O11 thin films on these electrodes and their ferroelectric properties will be discussed. The advanced two-step deposition technique has been used to improve the uniformity of the Pb5Ge3O11 film. Pure c-axis oriented Pb5Ge3O11 thin film and polycrystalline Pb5Ge3O11 thin film with preferred c-axis orientation and some Pb3GeO5 secondary phase have been successfully grown on these electrodes with good ferroelectric properties.

Ferroelectric C-Axis Oriented Pb5Ge3O11 Thin Films for One Transistor Memory Application

AbstractOne transistor memory devices have been proposed recently. To meet the needs of one transistor memory applications, C-axis oriented Pb5Ge3O11 (PGO) thin films were prepared using metalorganic chemical vapor deposition (MOCVD) and rapid thermal processing (RTP). It was found that the nucleation of C-axis Pb5Ge3O11 phase started at a deposition temperature below 400°C and grain growth dominated at 500°C or above. With increasing annealing temperature, the remanent polarization (Pr) and coercive field (Ec) values increased, and the hysteresis loops of the Pb5Ge3O11 films were well saturated and symmetrical after the post-annealing. The C-axis PGO thin film showed good ferroelectric properties at 5V: 2Pr and 2Ec values were 2.0 - 4.0 µC/cm2 and 90 - 110 kV/cm, respectively. The films also showed excellent fatigue characteristics: no fatigue was observed up to 1 × 109 switching cycles. The retention and imprint properties have also been studied. The leakage currents of the PGO films were 2 - 5 × 10−7 A/cm2 at 100 kV/cm and dielectric constants were 40 - 70. The high quality MOCVD Pb5Ge3O11 films can be used for single transistor ferroelectric memory devices.

Preparation and optical properties of gold-dispersed BaTiO3, PGO (Pb5Ge3O11) and PLT (Pb1–1.5xLaxTiO3) thin films by sol-gel process

Gold-dispersed BaTiO3, PGO and PLT thin films, which will be used for third-order nonlinear optical devices, were prepared by sol-gel process with spin-coating using HAuCl44H4O, Ba(CH3COO)2, Ti[O(CH2)3CH3]4, Pb(CH3COO)23H2O, Ge[O-n-C4H9]4, La(CH3COO)31.5H2O as starting materials. The thin films were heat-treated in air at temperatures ranging from 400 to 800 for 1 h. The nonlinear optical property of these thin films was measured by the degenerate four-wave mixing (DFWM) method using a frequency-doubled Nd : YAG laser with 20 ps pulse duration. Third-order nonlinear susceptibility χ(3) of gold-dispersed BaTiO3, PGO and PLT thin films with 5 vol% of gold were 1.410-6 esu, 3.510-7 esu and 1.010-7 esu respectively. The large χ(3) may be ascribed to the high dielectric constant of the films.

Preparation of Pb5Ge3O11thin films by multiple cathode sputtering

Abstract Pb5Ge3O11 thin films were prepared by multiple cathode rf-magnetron sputtering. PbO and the metal target of Ge were sputtered in an atmosphere of an argon and oxygen gas mixture. Pb5Ge3O11 thin films with preferred c-axis orientation were formed on MgO, Pt/MgO, Pt/SiO2/Si and RuO2/SiO2/Si substrates at 480 ∼490°C. An excess amount of lead compared to the stoichiometric ratio was required to compensate for the lead reevaporated from the substrate and to obtain a Pb5Ge3O11 single phase. Pb5Ge3O11 thin films deposited on the Pt/SiO2/Si substrate at 490 °C, then annealed at 600 °C exhibited dielectric anomaly at around 170 °C.

Processing of a uniaxial ferroelectric Pb5Ge3O11 thin film at 450 °C with c-axis orientation

Uniaxial Pb5Ge3O11 thin films were successfully fabricated by the sol-gel processing route. Crack-free and c-axis oriented thin films (1600 Å) were observed on (111) Pt-coated Si substrates when heat treated at 450 °C for 15 min. The thin films exhibited well saturated P-E hysteresis loops with Pr=3.3 μC/cm2, Ps=3.7 μC/cm2, and Ec=135 kV/cm. Specifically, a 1600 Å film switched at 2.2 V. The possible applications such as nonvolatile ferroelectric memories and CCD IR image sensors without fatigue or retention problems, are discussed.