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Cross-sectional HRTEM images of the MIM capacitors with different nanolaminated insulators consisting of (a) 1 nm Al 2 O 3 and 5 nm Hf O 2 , (b) 1 nm Al 2 O 3 , and 10 nm Hf O 2 . The insets show general views of the MIM capacitors. In image (b), the white and black ellipses show amorphous and crystalline Hf O 2 regions, respectively.
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Electrical characteristics of metal-insulator-metal capacitors with various Al2O3–HfO2 nanolaminates are investigated. The results indicate that the breakdown field decreases with increasing the HfO2 individual-layer (IL) thickness. Concerning the same dielectric composition, the insulator with a thinner HfO2 IL also exhibits a significant improvem...
Citations
... For instance, crystallization of a HfO 2 film is enhanced gradually with increasing its thickness under a maximum processing temperature of 420°C; i.e., 5 nm HfO 2 film is amorphous, 10 nm HfO 2 film is partially crystallized, and 58 nm HfO 2 film is fully crystallized. 60 Therefore, when we choose a high-κ dielectric as the blocking layer of the TFT memory, we should look for a high-κ film with a relatively high crystallization temperature (i.e., ≥400°C). In fact, this is not a real challenge for the oxide semiconductor TFT memory because the postannealing temperature is usually lower than 350°C, 5,22,23,35,38 which is used to adjust the carrier concentration in the oxide semiconductor channel so as to achieve good on/off current characteristics of TFT. ...
Charge-trapping nonvolatile memories based on amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) present unique merits for next-generation flexible and transparent electronic systems, however, the memory devices still face challenges, such as relatively high operating voltage, a slow operating speed, and insufficient data retention. The technology of atomic layer deposition (ALD) with many advantages is expected to overcome the challenges. In this perspective, the ALD fabrication processes and electrical characteristics of the AOS TFT memories are reviewed from the viewpoint of the device components, including a charge storage layer, charge blocking/tunneling layers, and an active channel layer. Meanwhile, for improving the performance of the memory devices, engineering design of device structures, materials and processes is further discussed by combining with the ALD technique.
... To optimize the electrical property of Ta 2 O 5 as gate dielectric, ultrathin Al 2 O 3 can be mixed into Ta 2 O 5 thin films for its current-blocking capability [14][15][16]. This composite structure is believed to provide a high dielectric constant and an acceptable leakage current by controlling the composition and structure [17][18][19][20][21][22][23]. ...
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Nanolayered Ta2O5-Al2O3 composite films were grown on n-type silicon by atomic layer deposition (ALD) within the overlapped ALD window of 220–270 °C. Moreover, post-annealing treatment was carried out to eliminate defects and improve film quality. Nanolayered Ta2O5-Al2O3 composite films remain amorphous after 700 °C annealing. The effects of composition, interface, and deposition sequence on electrical properties of Ta2O5-Al2O3 composite films were investigated in detail utilizing MIS devices. The results demonstrate that the formation of Ta2O5-Al2O3 composite films by mixing Al2O3 into Ta2O5 can decrease the leakage current effectively, but it leads to the decrease of the dielectric constant and the enhancement of the hysteresis effect. The interfaces in composite films are not conducive to prevent the leakage current. The deposition sequence of Si/(Al2O3/Ta2O5)n, Al2O3 as the first covering layer, reduces the leakage current and the hysteresis effect effectively. Therefore, the electrical properties of Ta2O5-Al2O3 composite films could be regulated by adjusting components and structures via ALD to acquire relatively great dielectric constants and acceptable leakage currents.
... High-permittivity (high-κ) metal-insulator-metal (MIM) capacitors have recently been studied for RF and analog/mixed-signal integrated circuits [1][2][3][4][5][6][7]. Among high-κ materials, HfO 2 is one of the most promising candidates due to high-κ (about 20-25) and large band gap (5.7 eV) [8][9][10]. However, a relatively high quadratic voltage coefficients of capacitance (α) remains as a serious dilemma for the application of the HfO 2 MIM capacitors, where the α is known to be inversely proportional to dielectric thickness and dielectric constant [11][12][13]. ...
... This indicates that the intermediate SiO 2 layer is very effective for improving the dielectric breakdown strength, because SiO 2 has an amorphous state and a large band gap (9 eV) in a universal IC process temperature range [14]. Ding et al. have reported that the crystallization of HfO 2 can be enhanced with increasing its thickness [8]. So with the introduction of the intermediate SiO 2 layer, the crystallization of HfO 2 can be suppressed and the grain boundaries (highly leaky paths) can be decreased, in order to lead to high electrical breakdown strength [19]. ...
... exhibits the typical plotting of ln (J) vs E 1/2 for the AHA and AHSHA capacitors under electron bottom injection according to the Schottky emission. It is observed that the experimental data can be well linearly fitting with Schottky emission model and the relative dielectric constants ( r ) for AHA and AHSHA dielectrics are deduced around 26.8 and 24.5, which are slightly larger than the previous calculated dielectric constant 18.4 and 11.9 by C-V measurement; while both of the deduced relative dielectric constants for AHA and AHSHA are over 30 with PF emission model (not shown here), which are far larger than values of theory and C-V measurement[8][9][10]. This result demonstrates the Schottky emission dominates the conduction for both of AHA and AHSHA capacitors, in agreement with the observation in AHA capacitor by Ding et al[4].1nm/5nm/1nm/5nm/1nm ...
... 16,17 Detailed studies of the conduction mechanism have been reported for several inorganic-based nanolaminates. 16,18 However, to date there have been no reports that have examined the leakage current mechanism(s) in hybrid nanolaminates comprised of alternating polymer and oxide thin films. We recently introduced hybrid nanolaminates comprised of alumina and silicone. ...
Alumina-silicone nanolaminates deposited by plasma-enhanced chemical vapor deposition were explored as dielectrics in metal-insulator-metal capacitors. Temperature-dependent current versus voltage (I-V) measurements were used to investigate the conduction mechanisms contributing to the leakage current in these structures. It is observed that space charge limited current mechanism is the dominant conduction process in the high field region. The estimated shallow trap level energies (Et) are 0.16 eV and 0.33 eV for 50% and 83.3% Al2O3 nanolaminates, respectively.
... A good example for future MOS technologies is HfO 2 , while a thickness less than 100 nm in silicon demands a gate dielectric other than SiO 2 [2]. With a high dielectric constant (20)(21)(22)(23)(24)(25) and a high band gap (5.1-6.0 eV) [3,4], it is compatible with polycrystalline silicon gate process and is also thermally stable with silicon [5]. The methods used to prepare HfO 2 thin films have a wide variety. ...
... This points out to the consistency between the conduction mechanism under high electric fields and Schottky emission. Another observation was that the extracted refractive index value gradually increases with increased measurement temperature, which may result from the effects of thermal stress, thermal expansion, and electronic polarizability [20][21][22]. The barrier height at the Al/HfO 2 and HfO 2 /p-Si interfaces was determined from 0.482 and 0.342 eV (100 K) to 0.936 and 0.778 eV (320 K), respectively. ...
The present study aimed to examine the current density-voltage (J-V) characteristics of Al/HfO2/p-Si (MOS) structure at temperatures ranging between 100 and 320 K and to determine the structure’s current transport mechanism. The HfO2 film was coated on a single side of the p-Si (111) crystal using the spin coating method. The J-V measurements of the obtained structure at the temperatures between 100 and 320 K revealed that the current transport mechanism in the structure was compatible with the Schottky emission theory. The Schottky emission theory was also used to calculate the structure’s Schottky barrier heights ( ϕ B ), dielectric constants ( ε r ) and refractive index values of the thin films at each temperature value. The dielectric constant and refractive index values were observed to decrease at decreasing temperatures. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of Al/HfO2/p-Si (MOS) structure was measured in the temperature range of 100–320 K. The values of measured C and G/ω decrease in accumulation and depletion regions with decreasing temperature due to localized N s s at Si/HfO2 interface.
... 14,15 As the measurement temperature increased, the value of n gradually decreased to a minimum of ϳ1.3, which was attributed to the effects of thermal stress, thermal expansion, and electronic polarizability. 14 Using the slopes of the ln͑J / E͒ versus 1 / T curves, we calculated the apparent trap energy levels ͓ t − ͱ qE / ͑ o r ͔͒ for the pure HfO 2 and Hf 0.36 La 0.64 O x as a function of the electric field ͓Fig. 3͑c͔͒. ...
Ultrathin HfO <sub>2</sub> and HfLaO <sub>x</sub> films with La /( Hf + La ) ratios of 42%, 57%, and 64% were synthesized with an atomic layer deposition process. By measuring the leakage current at different temperatures, the conduction mechanism of HfO <sub>2</sub> and HfLaO <sub>x</sub> films was shown to follow the Poole–Frenkel emission model under a gate injection condition. Based on the temperature and field-dependence measurements, the intrinsic trap energy levels were found to be 1.42, 1.34, 1.03, and 0.98 eV for the HfLaO <sub>x</sub> samples with La /( Hf + La ) ratios of 0%, 42%, 57%, and 64%, respectively, showing a decreasing behavior as the La content increased.
... 14,15 As the measurement temperature increased, the value of n gradually decreased to a minimum of ϳ1.3, which was attributed to the effects of thermal stress, thermal expansion, and electronic polarizability. 14 Using the slopes of the ln͑J / E͒ versus 1 / T curves, we calculated the apparent trap energy levels ͓ t − ͱ qE / ͑ o r ͔͒ for the pure HfO 2 and Hf 0.36 La 0.64 O x as a function of the electric field ͓Fig. 3͑c͔͒. ...
In situ current–voltage and capacitance–voltage characteristics were performed on Ni/HfO2/β-Ga2O3 devices using 120 MeV Ag⁷⁺ swift heavy ion (SHI) irradiation. The Poole-Frenkel emission is significant within 2.25–7.50 MV/cm until 5 × 10¹² ions/cm² and covers a full range of 0.01–7.50 MV/cm for the fluences of 1 × 10¹³ and 5 × 10¹³ ions/cm² under gate injection. The estimated trap energy level is Ec − 0.73 eV for pristine device whereas Ec − 0.65 eV is for 5 × 10¹³ ions/cm². Ni/HfO2 BH is 0.88 eV for the pristine device from Schottky emission. It is found to improve to 1.04 eV until 5 × 10¹² ions/cm² and then decrease to 0.75 eV at 5 × 10¹³ ions/cm² due to the athermal annealing. From Fowler-Nordheim tunneling, the BH of Ni/HfO2 interface is 0.78 eV and 0.69 eV at 1 × 10¹³ ions/cm² and 5 × 10¹³ ions/cm². X-ray photoelectron spectroscopy at O 1s reveals an increase in O defects within HfO2 due to electronic excitation.
We pioneered to employ room temperature atomic layer deposition (RTALD) to fabricate flexible Al-Ti-O based metal-insulator-metal (MIM) capacitors on three polymer substrates of polyethylene terephthalate (PET), polyimide (PI) and epoxy resin (epoxy) without any post-processing. Zn was introduced to Al-Ti-O dielectrics to tune its electrical properties through varying ALD cycle ratio and cycle number. Under the optimal processing, the flexible MIM capacitors of Al1.56Ti0.47Zn0.06O3 exhibits comprehensively better performance such as higher capacitance density of 7.4 fF/μm², smaller leakage current density of 2×10⁻⁸ A/cm² at 3 V, and reasonable quadratic voltage linearity of 422 ppm/V². X-ray photoelectron spectroscopy analyses reveal that the incorporation of a slight amount of Zn into Al-Ti-O dielectrics significantly decreases the oxygen vacancy concentration from 6.7% to 0.8%, beneficial for the improvement of electrical performance. Furthermore, our 2×2 cm² flexible MIM capacitors could bear 4000 bending cycles at bending radius of 8.2 mm, showing better electrical stability. These results indicate that RTALD-derived Al-Ti-Zn-O dielectrics are competitive MIM capacitor candidates for flexible electronics and wearable devices. RTALD technology exhibits exciting potentials in flexible electronic device fabrication.
Solution‐processed polar hydroxyl containing polymers such as poly(4‐vinylphenol) are widely utilized in organic filed‐effect transistors (OFETs) due to their high dielectric constant (k) and excellent insulating properties owing to the crosslinking through their hydroxyl groups. However, hydroxyl functionalities can function as trapsites, and their crosslinking reactions decrease the k value of materials. Hence, in this study, new solution‐processable copolymers containing both carboxyl and hydrophobic functionalities are synthesized. A fluorophenyl azide (FPA) based UV‐assisted crosslinker is also employed to promote the movement of polar carboxyl groups toward the bulk region and the hydrophobic functionalities to the surface region, thereby maintaining the high‐k characteristics and hydrophobic surface in thin film. Thus, the addition of an FPA crosslinker eliminates the trapsites on the surface, allowing a stable operation and efficient charge transport. Additionally, the solution‐processability enables the production of uniform and thin films to yield OFETs with stable and low‐voltage driving characteristics. The printed layers are also applied as gate dielectrics for floating gate memory devices and in integrated one‐transistor‐one‐transistor based memory cells, displaying their excellent memory performance. The synthesis and fabrication strategies employed in this study can become useful guidelines for the production of high‐k dielectrics for stable OFETs and other applications.
