Supporting Information for:
Electrically induced colossal capacitance enhancement
in LaAlO3/SrTiO3 heterostructures
Shuxiang Wu, Guangheng Wu, Jian Qing, Xiang Zhou, Dinghua Bao, Guowei Yang, and Shuwei Li
State and Key Laboratory of Optoelectronic Materials and Technologies, School of Physics
and Engineering, Sun Yat-Sen University, Guangzhou 510275, China.
Correspondence and requests for materials should be addressed to S. X. W.
(wushx3@mail.sysu.edu.cn) or S. W. L. (stslsw@mail.sysu.edu.cn).
Transport properties of LAO/STO interface
The transport properties of the conducting LAO/STO interface were measured in a Hall system
(Quantum Design) by using Hall-bar geometry. The temperature dependence of sheet resistance,
carrier density, and mobility of the LAO/STO interface are shown in Figure S1, which is consistent
with that reported by other leteratures1-2.
Figure S1:
(a) Temperature dependence of sheet resistance 10 u.c. LAO on TiO2
terminated STO substrate. (b) Temperature dependence of carrier density and mobility of
the LAO/STO interface
Thickness dependence of capacitance enhancement
(a) Quantum capacitance of LAO/STO heterostructure with 20 u.c. LAO film
In order to confirm the electrical control of quantum capacitance and colossal capacitance
enhancement, we also measure the C-V of LAO/STO heterostructure with 20 u.c. thick LAO film. In
the small gate voltage region, near depletion similar sharp peak of capacitance was observed at
frequency of 5 KHz at room temperature, as shown in Figure S2. As expected, the geometric
capacitance of capacitor device with 20 u.c. LAO film reduces by about 50% in comparison with that
of 10 u. c LAO film.
Figure S2: The capacitance (0.06 nF) of capacitor device with 20 u.c. LAO film is
around half of that (0.11 nF) of 10 uc LAO film as the thickness increases twice.
(b) Colossal capacitance enhancement of LAO/STO heterostructure with 20 u.c. LAO film
The capacitor device with 20 u.c. thick LAO film also show pronounced capacitance switching
behaviors at 5 KHz at room temperature, as shown in Figure S3. It can be seen the device exhibits
good retention and endurance, which is essential for the future application of oxide electronics. It
should be noted that the capacitance enhancement (more than 900%) of LAO/STO heterostructure
with 20 u.c. thick LAO film is larger than that (around 500%) of the sample with 10 u.c. thick LAO
film at 200 Hz. This result indicates that the sample with thicker LAO film shows larger capacitance
switching ratio. We suggest thicker LAO film could contain more mobile oxygen vacancies under
same gate voltage to the corresponding devices, which results in stronger response to AC signal.
Figure S3: Capacitance switching behaviors of the capacitor devices with 20 u.c. thick
LAO film. (a) When the amplitude of gate voltage is increased to 15 V, pronounced
hysteretic C-V curves are observed at 5 KHz at room temperature. (b) Frequency
dependence of capacitance enhancement. With the frequency decreasing, the high
capacitance state (HCS) is more sensitive to the AC signal with low frequency than low
capacitance state (LCS), corresponding to colossal capacitance enhancement, about 1000%
at 200 Hz. (c) Reliable bistable capacitance states are very stable during the successive gate
voltage sweeps, exhibiting a good endurance, and no performance degradation was
observed after 104 cycles of switching operations. (D) Both HCS and LCS are nonvolatile
with a good retention of more than 24 hours.
(c) Capacitance measurements of LAO/STO interface
To further understand the capacitance enhancement, we also measured the in-plane capacitance of
LAO/STO interface at 5 kHz, as shown in Figure S4. With the amplitude of gate voltage, the
capacitance decreases. This behavior is attributed to decrease of dielectric constant of STO substrate
with the applied voltage4,5.
Figure S4: C-V curve of 2 LAO/STO interface. The capacitance decreases, with the amplitude of
gate voltage. This behavior is attributed to decrease of dielectric constant of STO substrate with
the applied voltage.
Measurement of leakage current
It’s very important to measure the leakage at low frequency to confirm that the device based on
LAO/STO heterostructure is capacitor. Figure S5 shows the leakage conductance of the devices with
10 u.c. thick LAO films at room temperature, respectively. The devices have GΩ leakage at low
negative gate voltage, and as the negative gate voltage Vg is increased, the leakage conductance
increases greatly and appears a peak near the depletion. However, the devices generally have MΩ
leakage even at high gate voltage, which demonstrates that our devices based on LAO/STO
heterostructure are capacitor. This result is consistent with that reported by Lu Li et al.4.
Figure S5: Leakage conductance of the pristine devices with 10 u.c. thick LAO films at 20 Hz
at room temperature.
Impedance spectroscopy
Impedance spectroscopy is a technique that can separate the electrical components for electronic
conduction in dielectric films, including resistance, inductance, and capacitance. Here, we carried out
the impedance spectroscopy by applying a 30 mV AC small signal (20 Hz-10 MHz) via Keithley
4200 SCS semiconductor characterization system and Agilent 4284A LCR meter. Figure S6 (a)
shows the impedance measurement diagram of LAO/STO interface. It can be seen a semicircle in the
Nyquist plot (-Im(Z) vs Re(Z)) for the LAO/STO interface, as shown Figure S6 (b), which can be
fitted by the Cole-Cole function6:
Z
R
R 2C

j
1  R 2C 2
1  R 2C 2
Figure S6:
(a) LAO/STO interface configuration of measuring impedance spectroscopy.
(b) Nyquist plot (-Im(Z) vs Re(Z)) for the LAO/STO interface. (c) Capacitor device
configuration and equivalent circuit diagram for LCS and HCS. (d) Impedance spectra in
LCS and HCS exhibit two merged semicircles.
where R and C are the resistance and capacitance of material, respectively, and  is the angular
frequency. From the fitting impedance curve, the resistance of the LAO/STO interface is extrapolated
to be about 20 K, in agreement with sheet resistance measured in Hall-bar configuration at room
temperature (Figure S1). Furthermore, the impedance spectra in different capacitance states (HCS
and LCS) after applying sufficient positive/negative gate voltage were measured as shown in Figure
S6 (d). According to the impedance spectrum analysis, the equivalent circuit for LCS and HCS can
be modeled as schemed in Figure S6 (c).
Measurement of dielectric loss tangent in different capacitance states
Loss tangent measurement further confirms the characterization of capacitor, as shown in Figure 4 in
the manuscript. At low frequency in the range from 20 Hz to 200 Hz, the loss tangent is less than
0.05, and even at 1 kHz the loss tangent is about 0.1. It suggests that the leakage current of the
capacitor devices based on LAO/STO heterostructure is very small, which makes measured
capacitance convinced. According to the relationship of loss tangent tan=1/(2fRC), we can deduce
that the relationship of 1/(RC)= 2f tan. Thus we plotted the 1/(RC)~f curve in LCS and HCS,
which could rule out the possibility related to the variation of leakage current after application of
gate bias , as shown in Figure S7. As can be seen, the 1/(RC) increases in great amplitude with
frequency. In fact, the change of 1/(RC) is irrelevant to the frequency if the capacitance enhancement
is from the variation of leakage current, namely, the capacitance keeps constant after application of
gate bias, which is inconsistent with experimental results. Therefore, we conclude that the
capacitance switching is intrinsic, not from the variation of leakage current.
Figure S7. Frequency dependence of 1/(RC) in different capacitance states.
Procedure of measuring capacitance
Figure S8 shows the block diagram of a basic C-V measurement setup. The C-V measurements
Figure S8:
Inc.).
Block diagram of a basic C-V measurement setup (from Keithley Instruments,
are carried out at AC frequencies, and the capacitance of the device is calculated with the following:
C = I / (2πfVAC),
where I is the magnitude of the AC current through the device, f is the test frequency, and VAC is the
magnitude and phase angle of the measured AC voltage.
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