Performance and Reliability of Low-Temperature Processed SrBi[sub 2]Ta[sub 2]O[sub 9] Capacitors for FeRAM Applications

Abstract

Low-temperature processed SrBi 2 Ta 2 O 9 ͑SBT͒ capacitors were tested as the ferroelectric memory cells of fully functional ferroelectric random access memory ͑FeRAM͒ devices. The 100 nm thick SBT films were deposited by the spin-on coating technique using a metallorganic decomposition source and crystallized by rapid thermal annealing at 700°C for 1 min followed by a furnace annealing at 650°C for 1 h under oxygen atmosphere, considered a low thermal budget process. The fabricated Pt/SBT/Pt capacitors showed reasonable ferroelectric performances with a ⌬ P ͑switching polarization-nonswitching polarization͒ of approximately 10 C/cm 2 after the full process integration. The FeRAM chip-level reliability analysis showed that the major reason for the function failure was from the opposite state retention characteristics due mainly to the small ⌬ P values. A 10-year guaranteed lifetime can be achieved when the operation voltage is higher than approximately 4 V at the test condition of 85°C operation and 125°C storage.Ferroelectric random access memory ͑FeRAM͒ has attracted considerable attention due to its advantages of nonvolatile data retention, low power consumption, and fast write/read speed. 1 Among the many candidate ferroelectric materials, the SrBi 2 Ta 2 O 9 ͑SBT͒ thin film appears to be one of the most promising ferroelectric layer materials in the FeRAM due to its excellent reliability properties, such as fatigue and retention endurances, even with conventional Pt electrodes. 2 However, there are three major problems related to SBT material. The first is the high processing temperature ͑ϳ800°C͒ required for the crystallization of the material and recovery of the dry etching damage for integrated circuit formation. 3 The high processing temperature of the SBT material imposes various problems in FeRAM fabrication, especially for the merged memory-logic application, because the high temperature of the capacitor process adversely affects the transistor performances. This is true regardless of the integration density. When a high-density application is considered, the hightemperature annealing under the oxidizing atmosphere seriously oxidizes the buried contact of the capacitor having a capacitor-over-bit line structure, and malfunction of the device results.The second problem is the relatively small remanent polarization value ( P r , Ͻ10 C/cm 2 at 5 V applied voltage͒ compared to the Pb(Zr,Ti)O 3 ͑PZT͒ material, which shows a typical P r value of ϳ30 C/cm 2 at the same applied voltage. 4,5 Because the operation of FeRAM relies upon the amount of extracted charge from the cell capacitor, as in the case of dynamic random access memory, a smaller P r value, in principle, could induce a small sensing margin issue. Furthermore, unfortunately, the integration processes used for the FeRAM device after the ferroelectric capacitor fabrication generally degrade its performance. Usually, the P r decreases by the chemical interactions or the mechanical stresses imposed by the interlayer dielectric ͑ILD͒ and intermetal d...

CHARACTERIZATION OF IMPRINT BEHAVIOR FOR THE SrBi2Ta2O9 THIN FILMS

“…Ferroelectric random access memories (FeRAM) devices have attracted great attention as promising memory device due to their non-volatility, low power consumption and fast accessibility [1,2]. SrBi 2 Ta 2 O 9 (SBT) thin film is the most promising ferroelectric materials in the FeRAM due to its excellent reliability properties, such as fatigue and retention endurance, even with conventional Pt electrodes.…”

Etching Behavior and Damage Rejuvenation of Top Electrode and Bi3.15Nd0.85Ti3O12 Films Applied in Ferroelectric Random Access Memory Devices

“…F erroelectric random access memories (FeRAMs) have attracted considerable attention owing to their advantages of nonvolatile data retention, low power consumption, low operation voltage, and high write/read speed. [1][2][3] In particular, extensive research on PbZr x Ti 1Àx O 3 (PZT) and SiBi 2 Ta 2 O 9 (SBT) ferroelectric films as candidate materials for storage capacitors of highly integrated memory devices has been carried out. However, PZT films contain ''Pb'' and SBT films show a relatively low remanent polarization (2P r ) and require a high process temperature.…”