Energy Efficient Embedded Non-Volatile Memory & Logic Based on Ferroelectric Hf(Zr)O2

3eFERRO focuses on competitive, scalable FeRAM and logic-in-memory based on Si-compatible, ferroelectric HfxZr1-xO2. We report interface engineering, capacitor integration, FeFET and FeRAM logic design.

Energy efficiency

The 3eFERRO consortium researches energy efficient non-volatile memory and logic devices based on Si-compatible ferroelectric HfZrO2 (HZO) to provide advanced embedded solutions for normally-off microcontroller units used in IoT. The consortium is a balanced mix of large technology development laboratories and academia in partnership with ST Microelectronics to address the complex issues associated with materials optimization, circuit design, device fabrication and integration.

3eFERRO Video

3eFERRO partners realized a video presentation of the project to a wide audience, available here.

Reliability: zero bitfail in 16 kbit 1T-1C FeRAM arrays

Following the 16 kbit 1T-1C FeRAM new design, demonstrator #2 CMOS wafers with optimized sense amplifiers have been processed at CEA-LETI. 1T-1C FeRAM distributions were measured.

10 nm Si-implanted HfO2 is demonstrated to be ferroelectric for the first time when integrated in a Back-End-Of -Line (BEOL) 130 nm CMOS. Scaled 0.28μm² capacitors demonstrate excellent endurance (109 cycles measured at 4V, extrapolated to be 1012 at 3V), with tight coercive field distributions at wafer scale and excellent data retention at 85°C.

Zero bitfail has been recorded in the 16kbit 1T-1C array of the 600 nm. The Full ‘0’ and Full ‘1’ states are read after write operations adopting pulses of 2 µs width at 4.8 V. The test vehicle allows to address and read the individual bitcells. Patterns like the 3eFERRO logo can thus be stored in the array.

Charge injection in HfZrO2

There is a wide range of coercive fields quoted in the literature for HfO2 or HfZrO2 thin films. One reason may be the competing effects of applied bias and potential barrier set up by charge injection and trapping at defect sites. We have investigated this using piezo-response force microscopy and low energy electron microscopy to quantify the relative contributions of charge and domain switching to observations. Charge injection plays an important role in device reliability.

AlO and LaO electrical optimization of HfZrO2 films

Comparing both LaOx and AlOx interlayers, both showed improved leakage and cycling endurance, but AlOx decreased remanent polarization and degraded wake-up behaviour. This indicates that the best condition is still a 0.5 nm LaOx at the bottom TiN electrode. In addition, retention tests were performed on HZO based capacitors with AlOx or LaOx interface at elevated temperatures of 75°C.

A LaOx monolayer (about 0.5 nm LaOx) showed the highest pristine remanent polarization values and low wake-up effects compared to the uniformly mixed case. Looking at the best position of the LaOx monolayer, the interface between the bottom TiN electrode and HfZrO4 indicated lower fatigue. This result can be nicely seen as a clear cycling improvement with almost no wake-up effect in relation to the undoped and mixed doped case.