Improved Contact Resistance Research Articles

Contact resistance improvement using interfacial silver nanoparticles in amorphous indium-zinc-oxide thin film transistors

We describe an approach to reduce the contact resistance at compositional conducting/semiconducting indium-zinc-oxide (IZO) homojunctions used for contacts in thin film transistors (TFTs). By introducing silver nanoparticles (Ag NPs) at the homojunction interface between the conducting IZO electrodes and the amorphous IZO channel, we reduce the specific contact resistance, obtained by transmission line model measurements, down to ∼10−2 Ω cm2, ∼3 orders of magnitude lower than either NP-free homojunction contacts or solid Ag metal contacts. The resulting back-gated TFTs with Ag NP contacts exhibit good field effect mobility of ∼27 cm2/V s and an on/off ratio >107. We attribute the improved contact resistance to electric field concentration by the Ag NPs.

Predictive Simulation and Benchmarking of Si and Ge pMOS FinFETs for Future CMOS Technology

In this paper, we study and compare Si versus Ge pMOS FinFETs at advanced node dimensions using ensemble Monte Carlo simulations. It is found that due to large external resistance, lack of stressing methods, smaller bandgap, larger dielectric constant, and increased variability that in the absence of major innovation, Ge is not an ideal candidate for channel replacement material of pMOS in future CMOS technology generation FinFETs. In order for Ge to compete with Si, it would at a minimum require a stressing mechanism and improved contact resistance, but leakage and variability would still be a concern for low-power applications.

Microstructural evolution of wet deposited nickel interfacial phases on phosphorus doped silicon surface

Selective deposition and formation of Ni-Cu-Sn electrodes by electroless plating using an all-wet process were investigated to find a substitute for the commercial solar cells made by screen-printed Ag electrodes. Because of Ni-Cu-Sn multilayer, it is necessary to improve contact resistance at each interface using annealing process. So Nickel silicide was created by controlling the Si and Ni interface for the formation of an ohmic contact to reduce the contact resistance and improve the efficiency of solar cells. The phase transition and thermal stability of nickel silicide were analyzed in the annealing temperature range of 200–500 °C. Using electroless plated Ni, films with the thickness of 200±50 nm corresponding to the silicide phases of Ni2Si, Ni3Si2, and NiSi were identified from the thermal budget. The formation of the Ni74-Si26 silicide phase by rapid thermal processing at 250 °C was verified, and the possibility of low-temperature Ni silicidation was identified.

<inline-formula> <tex-math notation="TeX">${\rm MoS}_{2}$ </tex-math></inline-formula> Field-Effect Transistors With Graphene/Metal Heterocontacts

For the first time, n-type few-layer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> field-effect transistors (FETs) with graphene/Ti as the heterocontacts have been fabricated, showing more than 160-mA/mm drain current at 1-μm gate length with an ON-OFF current ratio of 107. The enhanced electrical characteristic is confirmed in a nearly 2.1 times improvement in ON-resistance and a 3.3 times improvement in contact resistance with heterocontacts compared with the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> FETs without graphene contact layer. Temperature-dependent study on MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /graphene heterocontacts has been also performed, still unveiling its Schottky contact nature. Transfer length method and a devised I-V method have been introduced to study the contact resistance and Schottky barrier height in MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /graphene/metal heterocontacts structure.

Optimized Contact Engineering to Maximize Cell Current in NAND Flash Memory Technology

In this research we have confirmed that Nand flash cell current increases by optimization of contact barrier metal (BM) deposition and plug implantation (IIP) doping condition, which result in improved contact resistance (Rc) and cell leakage. Plug IIP dopant, BF2, which has been applied to P-type Transistor (Tr) for lowering Rc sacrifices contact process margin in cell area of n-type occurred by cell leakage. We could dramatically improve P-type Contact Rc and contact process margin by lowering BM deposition process temperature and adopting plug IIP doping with phosphorous (Ph.) respectively

Effect of pre-cleaning treatment and contact wetting angle in the interface between P-doped Si surfaces and selective solar cell electrodes

Prior to electroless plating of the solar cell electrode, the sample was cleaned with a mixture of a sulfuric acid and peroxide solution and a H2NCH2CH2CH2Si(OC2H5) solution. We measured the de-wetting and contact angles of the solar cell thin film electrode. After SPM and APTES treatments, an excellent hydrophilic contact angle was observed. Our results show that it is more effective to remove oxidizer with SiO2 than HF mixed solutions. When comparing the efficiency, pre-treatment with a NH4F:HF mixed solution was more efficient than pre-treatment with a diluted HF solution. After NH4F:HF mixed solution cleaning, when the electrode was formed, the contact resistance that most directly affected the cleaning effect was 0.8194 ohm/sq, which had three times more improvement effect. It is expected that if an optimum cleaning time and process conditions for each cleaning chemical is developed, more improved contact resistance will be secured when each cleaning chemical is applied.

A study of the effect of compression on the performance of polymer electrolyte fuel cells using electrochemical impedance spectroscopy and dimensional change analysis

Compression plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). In this study, dynamic compression is applied using a cell compression unit (CCU) to study the effect on performance of a membrane electrode assembly (MEA) with dimension change. The stress/strain characteristics of the MEA are observed to be dominated by the gas diffusion layer (GDL), with the GDL exhibiting a degree of plasticity. Electrochemical impedance spectroscopy (EIS) is used to delineate the effect of compression on contact resistance and mass transfer losses. With increasing compression, a significant reduction in net performance is observed, with the most significant differences occurring in the mass transport regions of the performance curves. As the compression increases, the high-frequency resistance reduces with the improvement in contact resistance between the GDL and bipolar plate material, concurrently the low frequency resistance increases with increasing compression.

Contact resistance improvement by dielectric breakdown in semiconductor-dielectric-metal contact

We propose an approach for reduction of the contact resistance by inducing dielectric breakdown in a Si-dielectric-metal contact stack. We observe a 36% reduction in the contact resistance as well as an improvement in the uniformity in the distribution after dielectric breakdown. The results open up interesting device applications in complementary metal oxide semiconductor technology.

High Quality Silicon Cap Layer for 28nm and Beyond PMOS Processes

High quality embedded SiGe film with [Ge] concentration > 35% with Epitaxial grown Silicon (Si) cap layer has been demonstrated on a state-of-the-art 28nm logic flow. Si cap layer is a significant benefit to SiGe device for p-MOSFET contact resistance improvement but adversely affects the SiGe film strain relaxation especially for the high concentration [Ge] (> 35%). High quality, relaxation free SiGe film, with surface roughness improved from 4.21 to 0.65nm and 30% device contact resistance reduction are characterized in this work.

Nanomanufacturing Methods for the Reduction of Noise in Carbon Nanotube-Based Piezoresistive Sensor Systems

Carbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper, we will demonstrate several nanomanufacturing methods that can be used to decrease noise in the CNT-based sensor system without reducing the sensor's strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system, it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental effects. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. The optimal annealing conditions were determined using a design-of-experiments (DOE). Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost 3 orders of magnitude and increase the dynamic range of the sensors by 48 dB.

Co-doping of InxGa1−xAs with silicon and tellurium for improved ultra-low contact resistance

Abstract We report Te doping of bulk In 0.53 Ga 0.47 As up to 2.6×10 19 cm −3 without saturation effects, and structural characterization and contact resistances between metal and epitaxial regrowth for four structures: Si doped and Si and Te co-doped n + InAs regrowth on a 10 nm In 0.53 Ga 0.47 As channel, Si doped and Si and Te co-doped n + In 0.53 Ga 0.47 As regrowth on a 7 nm In 0.53 Ga 0.47 As channel. We observe that the contact resistance for the Si doped and Si and Te co-doped n + InAs regrowth on the 10 nm In 0.53 Ga 0.47 As channel is 9.9 Ω μm (3.9 Ω μm 2 ) and 6.6 Ω μm (2.3 Ω μm 2 ), and the contact resistance for the Si doped and Si and Te co-doped n + In 0.53 Ga 0.47 As regrowth on the 7 nm In 0.53 Ga 0.47 As channel is 8.5 Ω μm (2.3 Ω μm 2 ) and 6.8 Ω μm (1.9 Ω μm 2 ). The improvement in contact resistance comes from improvements in electron mobility consistent with Te improving material quality as a surfactant.

UV ozone treatment for improving contact resistance on graphene

Optimized UV ozone cleaning of graphene layers on SiO2/Si substrates is shown to improve contact resistance of e-beam evaporated Ti/Au contacts by three orders of magnitude (3 × 10−6 Ω-cm2) compared to untreated surfaces (4 × 10−3 Ω-cm2). Subsequent annealing at 300 °C lowers the minimum value achieved to 7 × 10−7 Ω-cm2. Ozone exposure beyond an optimum time (6 min in these experiments) led to a sharp increase in sheet resistance of the graphene, producing degraded contact resistance. The UV ozone treatment is a simple and effective method for producing high quality contacts to graphene.

Interface Modification of Cathode Electrode Using Dimmethyldicyanoquinonediimine as a Charge Transfer Layer in Organic Photovoltaic Cell

Various metals for the cathode electrode of organic electronic devices have been used in order to improve carrier injection and contact resistance etc. However, metal electrodes have some disadvantages such as rough surfaces, inadequate interfacial durability and unsuitable work functions. In the present work, we have fabricated an organic photovoltaic cell consisting of ITO/PEDOT:PSS/P3HT:PCBM/DMDCNQI/Al. The dimmethyldicyanoquinonediimine (DMDCNQI) compound was used as an organic n-type charge transfer complex between the cathode electrode and an organic active layer to improve contact resistance and electron transport ability. The prepared device shows a high short-circuit current density of 10.39 mA/cm2 and a maximum power conversion efficiency of 3.10%.

In situ TEM study on the improvement of contact resistance between a carbon nanotube and metal electrodes by local melting

Contact resistance between a multiwalled carbon nanotube (MWNT) and a metal electrode is governed by the contact structure. The relationship between the contact structure and electrical resistance was examined by in situ transmission electron microscopy using a nickel electrode and MWNTs with two kinds of tip structure; close‐capped and open‐ended. When the current density through the contact region reached a threshold value about 7.6 × 108 A/cm2, the MWNT tip was embedded below the nickel surface by local melting of the metal, and the contact resistance was reduced. In the case of the open‐ended MWNT, significant reduction of the contact resistance was observed, because inner shells of the MWNT with open cap can connect directly with the electrode. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Indium as an efficient ohmic contact to N-face n-GaN of GaN-based vertical light-emitting diodes

We propose indium (In), a low work function and nitride-forming element, as an efficient ohmic contact layer to N-face n-GaN. While conventional Al-based ohmic contacts show severe degradation after annealing at 300 °C, In-based ohmic contacts display considerable improvement in contact resistivity. The annealing-induced enhancement of ohmic behavior in In-based contacts is attributed to the formation of an InN interfacial layer, which is supported by x-ray photoemission spectroscopy measurements. These results suggest that In is of particular importance for application as reliable ohmic contacts to n-GaN of GaN-based vertical light-emitting diodes.

Adhesive-Free Transfer of Gold Patterns to PDMS-Based Nanocomposite Dielectric for Printed High-Performance Organic Thin-Film Transistors

Low-cost, adhesive-free direct transfer of gold patterns onto PDMS-based nanocomposite dielectric layer was investigated to significantly improve contact resistance at electrode-semiconductor interface in organic thin-film transistors (OTFTs). In particular, the nanocomposite film made from PDMS and solution-processable titanium dioxide nanoparticles was applied as dielectric layer in OTFTs, while transfer of gold patterns with a resolution lower than 3 μm is realized without use of any adhesive but through increased adhesion between gold and nanocomposite film of higher thickness and dielectric constant formed by in situ PDMS cross-linking process. Dielectric constant of the nanocomposite shows a dependence on the ratio of titanium dioxide nanoparticles to PDMS and the dielectric thickness was optimized for the best transfer efficiency. The organic transistors fabricated by this process demonstrate a high mobility of 0.038 cm(2)/(V s) and on/off ratio of 1 × 10(4) to 1 × 10(5). The electrode-semiconductor interface is evaluated by transmission line model to have width-normalized contact resistance of ∼100 kΩ cm while the inert property of dielectric-semiconductor interface gives low hysteresis (ΔV(th) = 1.2 V) and low threshold voltage (V(th) = -1.3 V) in the devices. This process can be readily adapted into a low-cost mass manufacturing process for printed organic electronics.

Improvement of contact resistance between carbon nanotubes and metal electrodes for high performance electronics

The authors developed a simple method that allows control of contact resistance between random network carbon nanotubes (CNTs) and metals such as gold and palladium to facilitate the development of high performance electronics on plastic substrates. The approach involves the deposition of a small amount of aluminum between random network CNTs and metal electrodes during the device fabrication process. The contact resistances of the resulting devices were measured, which showed that devices containing a thin layer of aluminum have lower contact resistances (Au: 1.086 kΩ μm and Pd: 2.282 kΩ μm) than devices without the layer (Au: 6.841 kΩ μm and Pd: 7.515 kΩ μm).

The Next Frontier: Electrodeposition for Solar Cell Fabrication

Electrodeposition for solar cells is an active area of research and it has been shown to provide improved benefits in several solar technologies. For the silicon solar cell contacts, electrodeposited metal contacts result in 1-2% solar cell efficiency improvement due to a lower processing temperature with better yield than screen printing, improved contact resistance, lower overall resistance, and the ability to fabricate smaller contacts that reflect less sunlight. This film electrodeposited chalcopyrite and kesterite offer very low-cost manufacturing. They can be used with rigid glass or flexible metallic substrates potentially opening up new applications for solar energy.

Noise Mitigation Techniques for Carbon Nanotube-Based Piezoresistive Sensor Systems

ABSTRACTCarbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper we will demonstrate several noise mitigation techniques that can be used to decrease noise in the CNT-based sensor system without reducing the sensor’s strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental variations. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost two orders of magnitude and increase the dynamic range of the sensors by 29 dB.

Interface Reactions between Conductive Ceramic Layers and Fe-Cr Steel Substrates in SOFC Operating Conditions

To improve contact resistance and protect the cathode from chromium poisoning, perovskite (La,Sr)CrO3, (La,Sr)CoO3 and spinel MnCo2O4 coatings were applied onto the surfaces of Fe-25Cr (DIN 50049) steel by means of the screen-printing method. The oxidation process of the coated steels under cyclic-oxidation conditions showed high compactness of the protective layer, good adhesion to the metal substrate, as well as acceptable area specific resistance level for SOFC metallic interconnect materials, which was the result of the structural modification of the coating/steel interface reaction, i.e. the formation of an intermediate, chromia-rich multilayer between the conductive coating and the metal substrate. The cross-sectional morphology and nanostructure of interface products formed during long-term thermal oxidation in air and the H2/H2O gas mixture at 1073K were characterized using SEM-EDS and conventional TEM-SAD. Cr-vaporization tests showed that the perovskite and spinel coatings may play the role of barriers that effectively decrease the volatilization rate of chromia species. [doi:10.2320/matertrans.MB201013]