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Correlation between the macroscopic ferroelectric material properties of Si:HfO2 and the statistics of 28nm FeFET memory arrays

: Mueller, S.; Slesazeck, S.; Henker, S.; Flachowsky, S.; Polakowski, P.; Paul, J.; Smith, E.; Müller, J.; Mikolajick, T.


Ferroelectrics 497 (2016), Nr.1, S.42-51
ISSN: 0015-0193
ISSN: 1563-5112
European Meeting on Ferroelectricity (EMF) <13, 2015, Porto>
Zeitschriftenaufsatz, Konferenzbeitrag
Fraunhofer IPMS ()

With the discovery of ferroelectric hafnium oxide (FE-HfO2), the ferroelectric field effect transistor (FeFET), a long-term contender for non-volatile data storage, has finally managed to scale to the 2x nm technology node. Here for the first time, we correlate the thickness dependent ferroelectric properties of Si:HfO2 with the memory characteristics of small (56bit) FeFET arrays. First, an electrical and structural analysis of metal-ferroelectric-metal capacitors is given. Even though possessing room-temperature deposited top electrodes, TiN / Si:HfO2 (20nm) / TiN capacitors are showing deteriorated polarization characteristics as compared to their 10nm Si:HfO2 counterparts. This could be attributed to an increased monoclinic phase fraction, as indicated by small-signal capacitance voltage and grazing incidence X-ray diffraction measurements. Identical Si:HfO2 thin films with thicknesses of 10nm and 20nm respectively, were utilized in a 28nm high-k metal-gate CMOS flow to form small FeFET memory arrays of AND architecture. After extracting the most suitable operating conditions from erase matrix, single cell evaluation was performed by standard V-P/3 program and a novel V-P/3 positive-source drain erase scheme. Array cells incorporating 10nm Si:HfO2 films showed a maximum memory window of 1.03 V whereas cells incorporating 20nm Si:HfO2 films could reach up to 1.57V. Moreover, in accordance to the basic material properties, the previously observed increased monoclinic phase fraction in 20nm Si:HfO2 thin films correlate well with a reduced number of functional FeFET cells.