Chen-Han Lin

Nanocrystalline ruthenium oxide embedded zirconium-doped hafnium oxide high-k nonvolatile memories

Metal–oxide–semiconductor capacitors made of the nanocrystalline ruthenium oxide embedded Zr-doped HfO2 high-k film have been fabricated and investigated for the nonvolatile memory properties. Discrete crystalline ruthenium oxide nanodots were formed within the amorphous high-k film after the 950 °C postdeposition annealing step. The capacitor with the Zr-doped HfO2 high-k gate dielectric layer traps a negligible amount of charges. However, with the nanocrystalline ruthenium oxide dots embedded in the high-k film, the capacitor has a large memory window. The charge trapping capacity and the trapping site were investigated using the constant voltage stress method and the frequency-dependent capacitance–voltage measurement. The memory function is mainly contributed by the hole-trapping mechanism. Although both holes and electrons were deeply trapped to the bulk nanocrystalline RuO site, some holes were loosely trapped at the nanocrystal/high-k interface. The current–voltage and charge retention results conf...

Nanocrystalline Silicon Embedded Zirconium-Doped Hafnium Oxide High-k Memory Device

Memory devices containing the nanocrystalline Si embedded Zr-doped HfO2 high-k dielectric film, which have many advantages over the conventional non-doped high-k films, have been prepared and characterized. The memory effect was manifested by the large counterclockwise capacitance–voltage hysteresis, e.g., 2.98 V, and negative differential resistance region in the positive bias current–voltage characteristics. A large memory operation window, e.g., 0.72 V, with a long charge retention time, e.g., >10,000 s, was achieved under the proper gate stress voltages. It is a viable dielectric for future nano-size metal oxide semiconductor field effect transistors and capacitors.

Nanocrystalline Zinc-Oxide-Embedded Zirconium-Doped Hafnium Oxide for Nonvolatile Memories

Memory devices containing nanocrystalline ZnO-embedded Zr-doped HfO 2 high-k dielectric film have been prepared and characterized. The memory effect was manifested by the large counterclockwise capacitance-voltage hysteresis, e.g., 1.22 at ±6 V gate bias, and negative differential resistance region in the positive bias current-voltage range. The maximum trapped charge density of 6.43 X 10 12 cm -2 was obtained after -9 → + 9 → -9 V sweep voltage range. The memory effects were mainly caused by electron trapping at low bias voltage. A large memory operation window, e.g., 0.90 V, with a long charge-retention time, e.g., >36,000 s, was achieved under the proper gate-stress voltage. It is a viable dielectric for future nanosize metal-oxide-semiconductor field-effect transistors and capacitors.

Memory Functions of Nanocrystalline Indium Tin Oxide Embedded Zirconium-Doped Hafnium Oxide MOS Capacitors

A floating gate metal-oxide-semiconductor capacitor memory device utilizing nanocrystalline indium tin oxide (ITO) layer embedded in a zirconium-doped hafnium oxide (Zr-doped HfO 2 ) high-k gate dielectric has been fabricated and studied. The embedded ITO layer has crystalline structure with a grain size of about 5.4 nm. Capacitance-voltage and current-voltage measurements show positive charge trapping under the negative gate bias operation condition. Comparison to a control sample shows a fourfold increase (5.3 X 10 -12 cm -2 to 1.4 X 10 -12 cm -2 ) in oxide trapped charge density and opposite trapped charge polarity, indicating that the observed effects are due to the inclusion of the ITO floating gate layer. The device maintains a large postwrite window (>100 mV) over a ten-year period. Furthermore, the prominent charge transfer mechanism is direct tunneling. The negative differential resistance in the current-voltage curve shows the existence of the coulomb blockade effect that may limit negative charge storing and retention. The asymmetrical barrier of the Zr-doped HfO 2 allows for the enhanced hole retention while eliminating the possibility of electron retention.

Charge detrapping and dielectric breakdown of nanocrystalline zinc oxide embedded zirconium-doped hafnium oxide high-k dielectrics for nonvolatile memories

Charge detrapping and dielectric breakdown phenomena of the nanocrystalline zinc oxide embedded zirconium-doped hafnium oxide high-k dielectric have been investigated. Charges were loosely or strongly retained at the nanocrystal sites which were saturated above a certain stress voltage. From the polarity change of the relaxation current, it was confirmed that the high-k part of the dielectric film was broken under a high gate bias voltage condition while the nanocrystals still retained charges. These charges were gradually released. These unique characteristics are important to the performance and reliability of the memory device.

Failure analysis of nanocrystals embedded high-k dielectrics for nonvolatile memories

Semiconducting and metallic nanocrystals have been embedded in high-k dielectrics for nonvolatile memories for advantages of low leakage currents, large charge storage capacities, and long retention times. However, there are few studies on the reliability issues, such as the breakdown mechanism and relaxation current decay rate. In this paper, authors investigated the reliability of four different kinds of nanocrystals, i.e., ruthenium, indium tin oxide, silicon, and zinc oxide, embedded in the Zr-doped HfO2 high-k thin film. Although all nanocrystals embedded samples have charge storage capacity about one order of magnitude higher than that without nanocrystals embedded samples, the formerpsilas relaxation currents are higher and decay times are longer than those of the latter. When the relaxation currents were fitted to the Curie-von Schweidler law, the formerpsilas n values were between 0.4 and 0.65, which are different from the latterpsilas n values of near 1. When the naocrystals embedded sample was broken under a high bias gate voltage stress, the high-k part failed while the nanocrystals remained unattacked. This is demonstrated by the lack of polarity change of the relaxation current. The time to breakdown of the high-k film was also extended due to the inclusion of nanocrystals in the film. Therefore, the embedded nanocrystals play an important role for the reliability of this kind of nonvolatile memory device.

Nonvolatile Memories Based on Nanocrystalline Zinc Oxide Embedded Zirconium-doped Hafnium Oxide Thin Films

Nanocrystals embedded dielectric structure has been proposed to replace the polysilicon floating dielectric structure for high-density nonvolatile memories [1]. The nanocrystals embedded dielectric can be easily fabricated into very small feature devices [2]. Nanocrystals, which can be made of different materials, enhance the trap and detrap electrons or holes in the dielectric layer [3-4]. Zinc oxide, which has a direct band gap of 3.2 eV, has been made into nanocrystalline dots (nc-ZnO) for optic and photovoltaic applications [5]. Based on the band diagram alignment of ZnO/Si, the ncZnO embedded gate dielectric should have better electron retention characteristic than that of the nc-Si embedded gate dielectric [6]. For sub 65 nm node MOSFETs, the high-k dielectric is required to replace SiO2 as the gate dielectric material to reduce the leakage current and to improve device reliability [7]. Recently, authors demonstrated that Zr-doped HfO2 has many improved electrical properties than the undoped HfO2 and can be prepared into sub 1 nm EOT film [8,9]. In this work, we fabricated the nc-ZnO embedded Zr-doped HfO2 MOS capacitors and investigated their memory functions.

Charge Trapping Sites in nc-RuO Embedded ZrHfO High-k Nonvolatile Memories

Materials and electrical properties of the MOS capacitor containing nc-RuO embedded in the high-k ZrHfO dielectric film have been studied. The electron- and hole-trapping capacities and trapping sites in this kind of device were investigated using the constant voltage stress method, the frequency-dependent C-V measurement, and the retention characteristics. The negligible charge trapping phenomenon in the non-embedded device rules out the possibility of any trapping site in the bulk ZrHfO film or at the Si/ZrHfO interface. The electrical characterization result suggests that electrons are trapped in the bulk nc-RuO. However, holes have two possible trapping sites, i.e., in the bulk nc-RuO or at the nc-RuO/ZrHfO interface.

Temperature Influence on Nanocrystals Embedded High-k Nonvolatile Memory Characteristics

The temperature influence on memory functions of the nanocrystalline ZnO embedded Zr-doped HfO2 high-k capacitor was investigated. Both the memory window and the trapped charge density increased with the increase of temperature. The temperature effect on hole trapping was observed at 125aC but not at 25aC or 75aC. The temperature effect on electron trapping was obvious above 25aC. The interface quality is greatly influenced by the temperature, which was detected on the C-V, G-V, and I-V curves. The sample temperature affects the carrier generation and transport mechanisms, which are responsible for the memory function changes.

Charge trapping of ultra-thin ZrHfO x /RuO x /ZrHfO x high-k stacks

Charge trapping in ultra-thin ZrHfO_x/RuO_x/ZrHfO_x high-k stacks has been investigated. ZrHfO_x/RuO_x/ZrHfO_x tri-layer may be a more proper high-k dielectric than ZrHfO_x, because of its smaller equivalent oxide thickness, leakage current and relaxation current. Positive charges trapped in both bulk and interface contribute to the interface state generation and V_fb, shift when electrons are injected from the gate under a negative gate bias condition; meanwhile no noticeable electron or neutral traps created by anode hole degrade much the performance of TiN/ ZrHfO_x/RuO_x/ZrHfO_x/p-Si. It was also observed that a negligible number of defects are generated until the gate bias stress increases to a certain level. The stress-induced trap generation is not reversible and the number of these newly generated traps could be comparable to or even larger than that of the pre-existed ones.