Supplementary information for
Grain size engineering for ferroelectric Hf0.5Zr0.5O2 films by an insertion of
Al2O3 interlayer
Han Joon Kim, Min Hyuk Park, Yu Jin Kim, Young Hwan Lee, Woojin Jeon, Taehong Gwon,
Taehwan Moon, Keum Do Kim, and Cheol Seong Hwanga
Department of Materials Science and Engineering, and Inter-university Semiconductor
Research Center, Seoul National University, Seoul 151-744, Korea
a
Email: cheolsh@snu.ac.kr
-Interplanar distance of (111) planes of orthorhombic phase
Table S1. d-spacing values from (111)-planes of orthorhombic phase of HfO2, ZrO2 and Hf0.5Zr0.5O2 films from
various studies.
Authors
Methods
Element
s
(111)
dspacing
(Å)
This work
XRD
HRTEM
Hf0.5Zr0.5O2
2.91
2.94
1995 JCPDS
Muller
et al
Lowther
et al
Kisi
et al
XRD
XRD
Ab initio
simulation
Neutron
diffraction
HfO2
Hf0.5Zr0.5O2
HfO2
ZrO2
ZrO2
2.94
2.94
2.98
2.96
2.96
- Microstructural analysis
Figure S1. The plan-view scanning electron microscope images of Hf0.5Zr0.5O2 films and
Hf0.5Zr0.5O2/Al2O3/ Hf0.5Zr0.5O2 films with various thickness. (D is the average grain size)
- Transient switching current analysis and role of Al2O3 layer
For the measurement, the pulse pattern generator and digital oscilloscope, whose internal resistances
are all 50 Ω, were serially connected to our ferroelectric capacitor. The schematic of the measurement
setup can be seen in figure S2a. The double remanent polarization (2Pr) values with increasing applied
voltage of the 10nm-thick HZO and 20nm-thick HZAHZ films measured by pulse switching
measurement system are shown in figure S2b. Both films had similar saturated 2Pr values, which was
consistent with P-E hysteresis in figure 3 of main text. Figures S2c and d show the transient switching
current-time curves using various pulse heights. The pulse width was fixed at 20 s, which was long
enough for complete polarization switching. In the initial stage of pulse switching, the capacitor
charging process occurred until the voltage across ferroelectric capacitor reached coercive value. After
that, the linear regions could be observed both for switching current-time curves of HZO and HZAHZ
films. Dashed lines were added to clearly show these regions. In this region, the transient switching
current could be formulated as:
𝑜
𝐼𝑆𝑊 (𝑡) = 𝐼𝑆𝑊
𝑒
−
𝑡−𝑡0
𝑅𝐿 𝐶𝑖
(𝑡0 ≤ 𝑡 ≤ 𝑡𝑠𝑤 )
(S1)
, where t0, tsw, RL, and Ci are the time when ferroelectric film starts to switch, the time when the
switching process is completed, total resistance of measurement circuit and sample, and interfacial
capacitance, respectively. The total resistance is the summation of the internal resistance of
pulse/pattern generator (50 Ω) and digital oscilloscope (50 Ω), parasitic resistance, and contact
resistance. It should be noted that the ferroelectric layer does not work as a resistor or capacitor in this
equation. When t is t0, the switching current can be formulated as:
0
𝐼𝑆𝑊
=
𝑉𝑎𝑝𝑝𝑙 −𝑉𝑐
𝑅𝐿
(S2)
, where Vappl and Vc are applied voltage and coercive voltage of ferroelectric layer, respectively.
Therefore, Isw0 – Vappl graph can be plotted from Isw(t0) values of transient switching current-time
curves with various pulse heights, and figure S2e shows the results. From the slope and x-axis
intercept of Isw0-Vappl curves, RL and Vc can be calculated. Based on the calculated RL values, Ci can
be finally calculated from the slope of linear region in ln(Isw)-t curve. With these steps, the RL and Ci
values of 10nm-thick HZO and 20nm-thick HZAHZ capacitors were calculated. The RL of 10nmthick HZO and 20nm-thick HZAHZ capacitors were ~137 and ~155 Ω, and their difference was ~18
Ω, which was similar to the resistance of 1nm-thick Al2O3 layer in our previous report (~15 Ω). [A. Q.
Jiang et al., Adv. Mater. 21, 2870 (2009)] On the other hand, the Ci of both samples were even larger
than 30 nF, meaning that the Al2O3 layer did not work as a series capacitor. If Al2O3 layer was a series
capacitor, the Ci value of HZAHZ capacitor should be smaller than its theoretical capacitance (~8nF,
assuming relative dielectric constant of 9 and 1nm thickness of Al2O3), but it was not the case. From
these results, it could be concluded that the Al2O3 layer works as a series resistor during ferroelectric
switching. Moreover, the large coercive field of HZAHZ capacitor might not results from the wide
distribution of switching current peak.
Figure S2. (a) Schematic diagram of the measurement system using a pulse generator and digital
oscilloscope (left panel), and shape of input pulse by the pulse generator (right panel). (b) Double
remanent polarization-electrical field hysteresis loop measured by pulse switching technique.
Transient switching current hysteresis of (c) the 10nm-thick Hf0.5Zr0.5O2 film and (d) the 20nm-thick
Hf0.5Zr0.5O2/Al2O3/ Hf0.5Zr0.5O2 film, respectively. (e) The initial domain switching current as a
function of the applied voltage hysteresis and the extracted resistance and (f) the extracted interfacial
capacitance of the 10nm-thick Hf0.5Zr0.5O2 film and the 20nm-thick Hf0.5Zr0.5O2/Al2O3/ Hf0.5Zr0.5O2
film.
- Endurance test
Figure S3. Endurance properties of Hf0.5Zr0.5O2 films and Hf0.5Zr0.5O2/Al2O3/ Hf0.5Zr0.5O2 films with
various thickness.