Top contacts

The transparent top contact is deposited last of all, which imposes restrictions on the process temperature. Thermally evaporated ITO and ZnO deposited by metal-organic CVD (MOCVD) are most suitable. At a typical thickness of 70 nm the ITO serves as a good antireflection coating as well. Due to the somewhat high sheet resistance, a metal (Ag) grid is necessary to reduce the series resistance [11]. 

An a-Si H-based position sensor consists of an intrinsic film sandwiched between two transparent conductive electrodes [637]. Two line contacts on the top are perpendicular to two on the bottom. When a light spot is incident on the device, carriers are generated, and a photocurrent flows to the contacts. The contacts form resistive dividers, so that from the ratio of the photocurrents the lateral position relative to the top or bottom contacts can be determined. The top contacts give the x-position, and the bottom contacts the y-position. 

Chang SC, Li ZY, Lau CN, Larade B, Williams RS (2003) Investigation of a model molecular-electronic rectifier with an evaporated Ti-metal top contact. Appl Phys Lett 83 3198... 

SAM-covered gold surfaces, these three peaks were assigned to Au-S, C-C, and C-H modes of surface-bound alkanethiolates [30]. The absence of a strong S-H signal at 329 mV suggests that most of the thiol groups have reacted with the gold bottom and top contacts. Peaks are also reproducibly observed at 80, 107, and 186 mV. We note that all alkanethiolate peaks, without exception or omission, occur in the spectra. 

Figure 4.8. Current voltage curves for selected A1PO capacitor structures. A high-quality thermally oxidized Si02 dielectric in an identical structure is included for reference. Top contacts are 0.011-cm2 A1 dots thermally evaporated via shadow mask. Bottom contact is made via conductive substrate p++ Si in the case of 600 °C A1PO and Si02 capacitors, and sputtered Ta metal for 300 °C A1PO devices.

The photovoltaic devices were then completed with a 50-nm layer of chemically deposited CdS, 50 nm of radio frequency (RF) sputtered intrinsic ZnO, and 350 nm of Al-doped ZnO and bilayer Ni/Al top contacts deposited by e-beam. Finally, a 100-nm layer of MgF2 is deposited by e-beam to minimize... 

The addition of In and Ga and selenization at high temperature were crucial in obtaining the 13.4%-efficient device. Photovoltaic device fabrication was completed by a CBD of about 500 A of CdS, followed by RF sputtering of 500 A of intrinsic ZnO and 3500 A of Al203-doped conducting ZnO. Bilayer Ni/Al top contacts were deposited in an e-beam system. The final step in the fabrication sequence is the deposition of lOOnm of MgF2 as an antirellection coating. 

Langmuir-Blodgett (LB) films for evaporation of top contacts without forming shorts due to defects in the LB structure. 

I can t actually figure out the operation of the device from the circuit that Slr9a9m9 supplied, but it is possible that there is another hidden coil wire, also, the operation of the rocker arm on the top contacts is hard to determine without knowing the spring loadings on the various contacts. I think it is pretty certain that there is nothing available today in the usual relay field which is even close. 

Strategies for Producing High Quality Top Contacts with No Shorts from... 

A perfect top contact would have a highly uniform layer of metal with complete, conformal contact at the SAM surface to form a sharp interface in which there is good overlap of the electronic states of the metal surface and the molecule terminal groups. This ideal situation is not to be expected in real device processing as a number of physical and chemical defects can easily arise, as summarized in the schematic in Fig. 6. 

While Pb is typically not a useful choice for device top contacts because of its low melting point and soft mechanical characteristics, it is of considerable interest for its superconducting characteristics. There appear to be, however, no reports on Pb deposition on SAMs. In our own preliminary experiments of Pb deposition on Cl6 alkanethiolate SAM on Au/mica from UHV AFM imaging, we observed complete penetration with no top surface cluster formation and continuing penetration into the underlying Au lattice. ... 

Kelvin-probe) AFM, and STM] to analyze the local phenomena and structure after top contact constmction. Development of new techniques such as surface plasmon resonance Raman, for example, could be applied to advantage for junctions fabricated with plasmonically active metals such as silver [125] or gold [126]. 

Lastly, and ultimately the most important, is evaluation of the applicability of the metal vapor top contact process for insertion into fabrication lines for mass production. At this point, significant improvements are required, well beyond the present state-of-the art, in order to achieve large cost efficient, high yield, high throughput fabrication. Hopefully, in the next decade, many of these issues will be resolved by the integrated research results from workers worldwide. 

Seitz O, Dai M, Aguirre-Tostado FS, Wallace RM, Chabal YJ (2009) Copper-metal deposition on self assembled monolayer for making top contacts in molecular electronic devices. J Am Chem Soc 131(50) 18159-18167... 

Aristov VY, Molodtsova OV, Ossipyan YA, Doyle BP, Nannarone S, Knupfer M (2009) Ferromagnetic cobalt and iron top contacts on an organic semiconductor evidence for... 

The coating chamber was equipped with a set of independently controlled stainless steel boats and a shutter system to enable the fabrication of multilayer structures. Pure selenium pellets were loaded into one boat and As Sei alloys into another. The two sources were evaporated sequentially (without breaking the vacuum) at boat temperatures of about 450 K. Typical coating rates were l j,m/min. After evaporation, they were allowed to anneal over several weeks in the dark at room temperature. During this period, due to structural bulk relaxation, most physical properties of the photoconductor film become stabilized. The compositions of the deposited films were determined by electron probe microanalysis, and the compositions quoted (0 < X < 0.20) are accurate to within 0.5 at.%. By shuttering the beginning and the end of the evaporation, a uniform arsenic composition across the film thickness can be obtained. In all experiments, a transparent gold electrode ( 300 jm thick) was used as the top contact. 

Enlargement of nanopore showing a small portion of the OPE SAM. Note that the thiolate-Au bond forms to the top contact due to the sequence of the process. 

While electrochemical experiments provide useful information regarding electron transport through these molecular monolayers, construction of real devices requires formation of a top contact so that solid-state transport measurements can be made. The fabrication of contacts to molecular layers has been the major obstacle to the development of molecular electronic devices, whether based on thiol-based SAMs on gold or covalently attached molecules on silicon. The most popular approach to making contacts involves evaporation of metals onto the molecular layer, which is likely to result in at least partial penetration of the monolayer, and may possibly damage the molecules in the layer. 

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