Memories
are important devices in semiconductor products. Our studies in this area are
focused on high-speed nanocrystals embedded high-k
memories and the novel low-temperature prepared floating-gate a-Si:H TFT memories. The capacitor
is a powerful basic device that can be used to investigate electric properties
including dielectric materials, interfaces, structures, and process influences.
We built MOS (or MIS) capacitors to screen new doped high-k
materials for future MOSFETs. We have also investigated nonvolatile memory
functions of the nanocrystals embedded high-k gate
dielectrics. We further research on the floating-gate
a-Si:H TFT nonvolatile
memories. The reliability of the new device, such as the deterioration
mechanism and lifetime under accelerated testing conditions, is an integrated
part of our research.
The
doped high-k film’s bulk and interface material, e.g.,
composition, concentration profile, thickness, bond states, and crystallinity, and electrical properties, e.g., interface
density of state Dit, oxide trap density Qot, fixed charge density Qf,
and flat band voltage Vfb, with respect to
dopant type, concentration, PDA condition, and
interface layer composition, have been investigated and reported, see Recent Publication list for details.
Nanocrystals embedded doped high-k
dielectric MOS memories
|
Q charge trapping density q electron charge. DVfb flat band voltage difference between Vfb of forward curve and that of backward
curve |
A. Birge and Y. Kuo, J. Electrochem. Soc., 154(10), H887 (2007).
· nc-Si embedded ZrHfO memory capacitors
J. Lu, Y. Kuo, J. Yan and C.-H. Lin, JJAP 45(34) L 901 (2006).
·
nc-ITO embedded ZrHfO2
- hole-trapping memory capacitors
Y.
Kuo, ECS Trans. 3(3), 253 (2006).
Y. Kuo, J. Lu, J. Yan, and C.-H. Lin, IEEE
Nano, 2006.
A. Birge, C.-H. Lin, and Y. Kuo, ECS Trans. 3(3), 193
(2006).
· nc-ZnO embedded ZrHfO – electron
trapping at low bias voltage
|
|
C-V curves for control and nc-ZnO
embedded capacitors at1MHz. |
-
Light illumination
provides a large amount of photon-generated electrons in the inversion
layer.
Slow electron trapping rate in darkness due to
limited supply of free electrons from p-type Si substrate and slow minority
carrier generation-recombination rate.
Figure
5. Flatband voltage
shift as a function of +6V gate stress time in the dark and under illumination
at room temperature.
-
Voltage dependent electron and hole trapping
Figure
6. Flatband voltage
shifts as a function of gate stress voltages for a 90s stress time measured in
darkness and at room temperature.
-
Excellent electron retention characteristics show that electrons
are deeply trapped at the nc-ZnO sites.
Figure
9. Charge retention of nc-ZnO
embedded ZrHfO after +6V 90s “write”, -7V, 10s erase,
and -8V, 10s “erase” conditions.
J. Lu,
C.-H. Lin, and Y. Kuo, ECS
Transactions, 11 (4) 509 (2007).
J. Lu,
C.-H. Lin, and Y. Kuo, J. Electrochem.
Soc. 155(6) H386 (2008).
Selected
AIP Virtual J. Nanoscale Sci. and Technology 17(7)
(2008).
· nc-RuO embedded ZrHfO – mainly
hole trapping below the ±6V gate bias region
- Holes strongly trapped at nanocrystal
site and loosely trapped at its interface
Fig. Ru 3d XPS spectra of (a) as-deposited and (b) after RTA at 950°C
under the 1:1 N2/O2 ambient for 1min.
|
|
Top view TEM |
Cross-sectional view
TEM |
Fig. Memory window and flat band voltage of nc-RuOx embedded ZrHfO
capacitors.
Fig. J-V curve swept from 0V to –5V then back to 0V.
Polarity of current flow: positive (to substrate) or negative (to gate).
|
|
Fig. (a) C-V (at 1MHz) curves after stressed at
different negative (-5V to –10V) and positive (+5V to +10V) gate voltages and
(b) shift of Vfb as a function of the
gate stress voltage. The stress time was fixed at 5s. |
|
|
Fig. G-V curves measured at 1M, 500k, and 100kHz
with different gate voltage sweep voltage ranges of (a) control sample and
(b) nc-RuO embedded ZrHfO
capacitor. |
C.-H. Lin and Y. Kuo, ECS Transactions, 13(1) 465 (2008).
C.-H. Lin and Y. Kuo, ECS Transactions,
16(5), 309 (2008).
· Dual-layer nanocrystals
embedded ZrHfO
|
|
|
(a) ZrHfO control sample. |
(d) single-layer
nc-ZnO embedded ZrHfO |
(e) dual-layer nc-ZnO embedded ZrHfO |
C.-H. Lin and Y. Kuo, ESL,
13(3) H83(2010).
|
|
Fig. C-V hysteresis curves of control, single-, and
dual-layer nc-ZnO embedded samples measured at 1 MHz. |
Fig. Shifts
of VFB wrt fresh single- and
dual-layer nc-ZnO embedded ZrHfO
vs. stress time at Vg = +8 V. |
Fig. C-V curves of nc-ITO and nc-ZnO embedded capacitors stressed at –8V or +8V for 10ms:
(a) single nc-ITO, (b) dual nc-ITO,
(c) single nc-ZnO, and (d) dual nc-ZnO
embedded in ZrHfO. The measurement was done by
sweeping voltage from –2V to 1V.
Fig. Change of Vfb
with gate stress time of single and dual (a) nc-ITO
and (b) nc-ZnO embedded ZrHfO
capacitors. The gate bias voltage was fixed at -8V for nc-ITO
and +8V for nc-ZnO embedded samples, respectively.
· Reliability – relaxation and breakdown mechanisms
-
higher relaxation
currents than the non-embedded high-k film
|
|
|
Fig. Relaxation current density vs
time of nc-ZnO embedded ZrHfO
capacitor and control sample. |
Fig. Relaxation
current normalized to polarization vs time of nc-ZnO embedded ZrHfO and
various high-k and SiO2 dielectrics. |
Curie-von Schweidler equation
J / P = at –n
J: relaxation current density (A/cm2), P: total
polarization or surface charge density (V·nF/
cm2), t: time in
second,
a: a constant, n: a real number 0 < n
< 1
C.-H.
Yang, Y. Kuo, and C.-H. Lin, Appl. Phys. Letts., 96, 192106 (2010). |
-
nanocrystals retain charges in deeply and loosely trapped states
Table. Percentages
of deeply and loosely trapped charges for nanocrystal
embedded samples after the first 20 seconds.
-
breakdown from
the bulk high-k film
nc-Ru nc-ZnO nc-ZnO nc-Ru nc-ITO
& -Si nc-ITO
& -Si
Fig. Ramp-relax
test results on nanocrystals embedded high-k films
C.-H. Yang, Y. Kuo, C.-H. Lin, R. Wan, and W. Kuo, MRS Procs. 1071-F02-09 (2008).
C.-H. Yang, Y. Kuo, R. Wan,
C.-H. Lin, and W. Kuo, IRPS
46 (2008).
· Reliability –breakdowns of single- and dual-layer nanocrystals embedded high-k
|
|
|
Fig.
(a) Jramp-Vg and (b) Jrelax-Vg and (c) C-V curves of a
single-layer nc-ITO embedded ZrHfO
capacitor measured with the two-step ramp-relax method. |
C.-H. Lin and Y. Kuo, ECS Transactions,
19(8), 81 (2009).
C.-H. Lin and Y. Kuo, Electrochem. Solid-State Letts.
13(3) H83 (2009).
· Reliability –Temperature Influence on Nanocrystals Embedded High-k Nonvolatile C–V
Characteristics
|
Fig. C–V hysteresis
curves for (a) control sample at 25°C, (b) nc-ZnO
embedded ZrHfO at 25°C, (c) nc-ZnO
embedded ZrHfO at 75°C, and (d) nc-ZnO
embedded ZrHfO at 125°C. C.-H. Yang, Y. Kuo, C.-H. Lin, W. Kuo, ESL 14(1),
H50 (2011) |
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