Charge Trapping and Detrapping in nc-RuO Embedded ZrHfO High-k Thin Film for Nonvolatile Memory Applications

Abstract

The charge trapping and detrapping characteristics of the nc-RuO embedded Zr-doped HfO 2 (ZrHfO) high-k MOS capacitor have been studied. The memory function of the capacitor is mainly contributed by hole trapping during the forward sweep from −9 V to +9 V and electron trapping during the backward sweep from +9 V to −9 V. The time-and bias-dependent stress test results show that the hole-trapping efficiency is higher than the electron-trapping efficiency due to different charge trapping sites and supply mechanisms. In order to delineate the detailed mechanisms, samples were characterized with the frequency-dependent conductancevoltage curves, relaxation currents, ramp-relax current measurements, and retention characteristics. Although most electrons are deeply trapped in the bulk nc-RuO sites, a portion of holes are loosely trapped at the nc-RuO/ZrHfO interface due to the lost of the short-term retention capability. The deeply-trapped holes and electrons were strongly held for a long period. The nanocrystals embedded high-k thin film is a potentially important gate dielectric structure for the high-density floating-gate nonvolatile memory due to the high charge storage capability, low operation power, and long retention time.1-3 Based on the same equivalent oxide thickness (EOT), the HfO 2 high-k film has a thicker physical thickness than SiO 2 . In addition, HfO 2 has lower electron and hole energy barriers with respect to Si than SiO 2 , i.e., 1.5 eV and 3.4 eV, vs. 3.5 eV and 4.3 eV, respectively. 4 Previously, it was reported that the sputter deposited Zr-doped HfO 2 (ZrHfO) film showed a higher amorphous-to-polycrystalline crystallization temperature and better interface quality than the undoped HfO 2 .5 An ultra thin ZrHfO layer, e.g., EOT∼1 nm, was successfully prepared into a MOS capacitor. 6 Separately, it has been demonstrated that conductive materials, such as metals, indium tin oxide (ITO), or zinc oxide (ZnO), can be prepared into the nanocrystalline (nc) form and embedded in the high-k film as the electron-or hole-trapping medium.7-9 The charge trapping characteristics in this kind of device are closed related to the embedded nanocrystal material. For example, the nc-ITO embedded device prefers to trap holes while the nc-ZnO embedded device traps electrons or holes depending on the polarity of the gate voltage. 8, 9 Ruthenium oxide (RuO) is a conductive oxide with excellent diffusion barrier quality, good chemical and thermal stability, and a high work function (∼5 eV), which makes it a good deep charge trapping medium in the dielectric film.10-13 Previously, Maikap et al. 14 reported that nc-RuO could be included in the HfO 2 /Al 2 O 3 high-k film using the atomic layer deposition (ALD) method. Authors have also demonstrated that excellent memory functions were obtained with the nc-RuO embedded ZrHfO film prepared by the sputter deposition method followed by a post deposition annealing (PDA) step.15 Although the basic memory function has been demonstrated, the detailed charge trapping and retention...

Memory functions of nanocrystalline cadmium selenide embedded ZrHfO high-k dielectric stack

“…The exchange of the holes between the nc-CdSe/ZrHfO interface and Si wafer reduces the energy loss, which causes the larger drop of the conductance peak. 43 The C-V and G-V responses to the frequency dispersion are consistent with the CVS result and the band diagrams.…”

“…At the low measurement frequency, interface traps could keep pace with the ac signal change, which reduces the energy loss of the capacitor. [42][43][44] The smaller energy loss induces the lower conductance peak. The decrease of the conductance peak height in the G-V curves from À6 V to þ6 V is more pronounced than that in the G-V curves from þ6 V to À6 V, e.g., by two times.…”

Nonvolatile Memory Characteristics of Nanocrystalline Molybdenum Oxide Embedded High-kFilm - Device Performance and Light Wavelength Effects

“…Therefore, charges were still retained on the nanocrystal site even the bulk high-k film was broken. This kind of unique property has been observed in nc-ZnO and nc-RuO embedded dielectric structure [17,18]. Light wavelength effect on charge trapping and detrapping characteristics Figure 4 shows the C-V hysteresis curves of a thin nc-MoO x , i.e., deposited for 15 sec, embedded ZrHfO capacitor measured in the dark and under the red and blue LED lights, separately.…”

“…The first peak in the backward curve near V g = 0 V is due to the release of holes due to the change of the gate polarity. The second peak is related to the Coulomb blockade phenomena, which is commonly observed in the nanorcrystals embedded dielectric or other floating-gate structures [16][17][18][19].…”

Nonvolatile memory devices with AlOx embedded Zr-doped HfO2 high-k gate dielectric stack

“…18 Holes can be trapped at the tunnel ZrHfO/AlO x interface, the AlO x layer, the AlO x /control ZrHfO interface, or the control ZrHfO layer. The exchange of the holes reduces the energy loss, 27 which causes a large drop of the conductance peak. 15,19 The AlO x layer contains certain hole-trap sites.…”