Imec has developed a high-endurance ferroelectric capacitor that it is describing at this week’s International Electron Devices Meeting in San Francisco that the researchers will be useful for embedded memory on SoCs and standalone non-volatile devices though it falls slightly short of the target needed for storage-class memories in its current state.
The team used a lanthanum-doped hafnium-zirconate (La:HZO) material as the core capacitor material, obtaining an endurance of 1011 cycles, versus a target of more than 1012, and a final (2PR) polarization of 30µC/cm2 at 1.8MV/cm. The main changes they made in constructing the experimental capacitor were to the interfaces between oxide layers in the stack.
The problem with HZO capacitors up to now has been the inability to maintain polarization above 30µC/cm2 over the device’s useful lifetime, either because they suffer from “slow wakeup” where the polarization does not reach high enough levels until after a number of cycles or because they age out too soon.
“By interfacial oxide engineering, adding both a 1nm TiO2 seed layer and 2nm Nb2O5 cap layer to the La:HZO layer, we achieved for the first time high endurance in combination with a final 2PR as high as
~30µC/cm2 and good initial 2PR,” said Jan Van Houdt, program director of ferroelectrics and a fellow at Imec.
An alternative precursor for depositing the HZO led to higher 2PR but an endurance five orders of magnitude lower.
“Now we have a high-performance, scalable, and CMOS-compatible ferroelectric capacitor technology that will bring us to the next exciting phase, that is, moving from planar to 3D FeRAM capacitor structures – leveraging atomic layer deposition (ALD) processes,” said Van Houdt. “This will increase the density needed to bring FeRAM memories to the market as a new embedded or standalone memory.”