The interfacial trap density (Dit) is two orders of magnitude higher than the SiO2/Si. For the Schottky barrier diode, the Schottky barrier height is a very important parameter to determine the characteristic of the device.
Silicon Carbide
Crystal Structure
Electrical Properties of Silicon Carbide
Spontaneous Polarization
Where is the scaling factor for the hexagonal crystal, p is the Si-C bond polarity, m is the Si-C bond metallicity, c 12p is the Si-C bond covalency and d is the Si-C bond length.
Schottky Junction
- Energy Band
- Metal/semiconductor Junction
- I-V Characteristic
- C-V Characteristic
- Internal Photoemission Measurement
- Measurement Setup
Where N(E) is density of states and F(E) is distribution function, then the current density can be expressed as the following equation. According to Powell's model, the quantum yield is calculated as follows, and the electron energy barrier can be obtained from the quantum yield threshold.
Atomic Structure
Aluminum nitride (AlN) is an emerging material due to its superior properties in wide band gap (e.g. = 6.19 eV), high thermal conductivity, high decomposition temperature and high dielectric constant. AlN is used for optoelectronic applications including UV detectors, short wavelength transmitters, short wavelength detector and lasers. 25] There are few reports on SiC/AlN MISFET, but they were far from practical use due to their high gate leakage and high resistance.
Electrical Properties
Fabrication of Aluminum Nitride Thin Film
Thin Oxide Remove
Natural oxide can increase the interfacial trap density, which significantly deteriorates the channel mobility of SiC. The UHV chamber consists of a loading lock chamber and a main chamber, as shown in Figure 18. Before the sputtering process, an in-situ annealing process at 620 ℃ for 5 minutes is carried out to remove native oxide.
RF Sputtering
Furthermore, Huang, L explain the mechanism of Schottky barrier increase by increasing interface trap density. Tsui, B.-Y., et al., Schottky barrier height modification of metal/4H-SiC contact using ultrathin TiO2 insertion method. Nicholls, J., et al., Description and verification of the underlying current mechanisms in silicon carbide Schottky barrier diodes.
Xu, R.L., et al., Thermal conductivity of crystalline AlN and the influence of atomic-scale defects. Coss, B., et al., Height modulation of the Schottky barrier near the band edge using a high-κ dielectric dipole tuning mechanism. Gülen, Y., et al., Height adjustment of the Schottky barrier in Au/n-type 6H-SiC structures by PbS interfacial layer.
Coss, B.E., et al., Reduction of contact resistance to FinFET source/drain using a novel dielectric dipole Schottky barrier height modulation method. Huang, L., et al., Modulating Schottky barrier of metal/p-type 4H-SiC by intercalation of insulator TiO2 thin layers.
Thermal Annealing
SiC Schottky Diode
The fringe electric field at the top electrode is affected by the dielectric constant of the finger. Khosa, R.Y., et al., Electrical properties of 4H-SiC MIS capacitors with MOCVD-grown AlN gate dielectrics. Potbhare, S., et al., Numerical and experimental characterization of 4 H-carbide lateral metal-oxide-semiconductor silicon field-effect transistor.
Chung, G., et al., Effect of nitrogen oxide annealing on the interface drop density near the band edges in the 4H polytype silicon carbide. Sochacki, M., et al., Interface traps in Al/HfO2/SiO2/4H-SiC metal-insulator-semiconductor (MIS) structures studied by the thermally stimulated current (TSC) technique. Lee, H., et al., Moving beyond flexible to stretchable conducting electrodes using metal nanowires and graphene.
Wang, J., et al., High efficiency transfer from percolating nanowire films for stretchable and transparent photodetectors. Kim, J.S., et al., Controlling the electrode work function and active layer morphology via surface modification of indium tin oxide for high efficiency organic photovoltaics.
Ni/4H-SiC Schottky Barrier modulation by AlN Layer
I-V Measurement
The bare Ni/SiC sample has a Schottky barrier of 1.721 eV and the barrier decreases as the sputtering time increases. After 120 seconds, the barrier increases considerably and the ideality factor becomes higher, and the current density decreases significantly. There is a report that a thin layer of PbS between Au/6H-SiC Schottky diode reduces the Schottky barrier by 0.09 eV [52], a thin layer of TiO2 between Ni, Ti, Al/4H-SiC Schottky diode also reduces the barrier by 0.2 ~ 0.3 eV, but significantly increases the reverse leakage current.
After more than 150 seconds of deposition, the Schottky barrier increased even more and shows a very strange curve of plot. As the thickness increases, the current density tends to decrease but almost the same up to 90 sec. The reverse leakage current is below the limit for the SMU 2636A which has 10-13's minimum current resolution and the current density was calculated with 500 um diameters of circle.
The current is measured with hysteresis with 530 ms delay and 0.01 mV step to reduce the noise. Extract Schottky barrier and ideality factor by I-V measurement with respect to the aluminum nitride deposition time.
C-V Measurement
IPE Measurement
Schottky Barrier
When the application time is longer than 150 seconds, the current is greatly reduced and the capacitance is such an unusual change that the barrier could not be eliminated. There are potentially three mechanisms to explain the reduction in Schottky barrier height, depinning at the Fermi level by reducing the surface interaction, [59] formation/screening of dipoles at the dielectric/semiconductor interface, and reduction of the fixed oxide charge. Extracted Ni/AlN/4H-SiC Schottky barrier with I-V, C-V and IPE measurements versus AlN sputtering time.
Transmission Electron Microscopy
Metal-insulator Gap State
Fermi-level Depinning
Screening of Interfacial Dipole
SiC MOSFET Structure
UMOSFET
I-V Characteristic
Silver Nanowires
It is required to achieve high conductivity for the transparent electrode in accordance with the great interest of variable optoelectronic devices such as touch screen panels, organic light-emitting diodes and organic photovoltaics. 78-83] In recent decades, indium tin oxides (ITOs) have dominated in optoelectronics research and industry, due to their superior performance of both electrical and optical properties. 80, 86] The candidates for the emerging transparent electrodes are conducting polymers, graphene, carbon nanotubes and metal nanowires.
In particular, the silver nanowires (AgNWs) are one of the most attractive materials due to their excellent electrical conductivity, which is comparable to ITOs. 89] Silver, having an exceptional electrical conductivity (6.3 × 10 S m ), provides high performance even when used in nanowires as thin as several tens of nanometers in diameter, which are almost invisible to the naked eye. Furthermore, AgNWs can be easily deposited by coating process, while ITOs require sputtering and annealing processes.
93] A longer length of AgNWs, so-called silver nanofibers, can be used to reduce the effect of contact resistance, but a shorter length of AgNWs is favorable for raising the persistence of conduction in transformation. 94] Therefore, it is very important to reduce the contact resistance for the commercialization of AgNWs for a transparent electrode.
Compression-assisted Plasmonic Welding
Plasmonic Welding
Sample Fabrication
Electrical Properties
When the AgNWs are coated 5 times on the substrate, transparency is about 89% at the wavelength of 570nm. Due to the random network property of nanowires, there may be a disproportionate amount of AgNWs on the substrates. The catch is that the formation of numerous small round lumps of silver on the silver nanowire.
On the contrary, Figure 47 (c), (d) which are the SEM images of AgNWs after compression-assisted UV welding, shows a clear distinct image compared to the image of the conventional welding samples. 81, 114] Display fingerprint sensors are one of the successful examples of such bionic sensors equipped with TSP. When the finger touches the surface of the TSP, a certain part of the electric fields generated by the transmitter electrode (TX) is absorbed by the finger and the mutual capacitance between the transmitter electrode and the receiver (RX) decreases so that the finger touch can feel
114, 121] Here, the periodic behavior of blood flow during cardiac cycles regularly modulates the dielectric constant of the finger. On the other hand, if TX and RX are placed laterally, the effect on the dielectric on the edge electric field is much greater. In addition, because the penetration depth of the electric field is proportional to the distance between the TX and RX electrodes, it is adjustable to find the point where the heart rate signal is maximum.
Fabrication Processes of Multilayer Structure TSP
Touch Sensing
Heart-Rate Sensing
The spacing between interdigital electrodes is proportional to the penetration depth which is the depth the field can reach. Conventional skin moisture sensor uses the spacing of micrometer scale to allow penetration depth to reach the stratum corneum distributed in 10 μm of the skin. In this scheme, if the spacing between interdigital electrodes increases to a few millimeters, it is possible to achieve penetration depth to blood vessel whose volume changes periodically.
We adopted this principle in the TSP and it allows the detection of the change in permeability of the finger in relation to the heart rate. In the operation of the designed capacitive TSP, the lower electrodes are used as RX and the upper electrodes are used as TX. As the dielectric material approaches the top electrode, the capacitance between the top and bottom electrodes decreases because the dielectric material absorbs the electric field generated by the TX.
Here the dielectric effect is negligible enough to be indistinguishable from noise, because most of the electric fields affected by the dielectric are absorbed by the finger. For this configuration, the difference from conventional TSP is that the upper electrodes are separated into two parts and arranged alternately with respect to each other.
Signal Processing
Seppänen, H., et al., Aluminum nitride junction layer for power electronics applications grown by plasma-enhanced atomic layer deposition. Strak, P., et al., Polarization and polarization induced electric field in nitride critical evaluation based on DFT studies. Kluth, O., et al., Comparative materials study on RF and DC microwave sputtered ZnO:Al films.
Cremer, R., et al., Comparative characterization of alumina coatings deposited by RF, DC and pulsed reactive magnetron sputtering. Gillinger, M., et al., Effect of annealing temperature on the mechanical and electrical properties of sputtered aluminum nitride thin films. Jeon, Y., et al., Highly flexible touchscreen panel fabricated with silver nanowire crossing electrodes and transparent bridges.
Ma, H., et al., On-display transparent half-diamond pattern capacitive fingerprint sensor compatible with AMOLED display. Oresko, J.J., et al., A wearable smartphone-based platform for real-time cardiovascular disease detection via electrocardiogram processing.
Extraction of Heart-Rate with a Protective Layer Covering for High-Resolution
