Bottom contact

Fig. XII-12. Top friction traces for two calcium alkylbenzenesulfonate monolayers on mica where the monolayers are in a liquidlike state. A—in inert air atmosphere B—in saturated decane vapor. Bottom contact radius-load curves showing adhesion energy measured under the same conditions as the friction traces. (From Ref. 53.)...

The top conductor is almost always in a grid-pattern to allow as much area as possible open to contact with light photons. Note that metals are not light-transparent. The bottom contact does not need to be patterned. 

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. 

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.

Other device architectures include inverted OLEDs. Here the cathode is in intimate contact with the substrate. The organic layers are then deposited onto the cathode in reverse order, i.e., starting with the electron transport material and ending with the HIL. The device is completed with an anode contact. In this case, as above, one of the electrodes is transparent, and light exits from the device through that contact. For example, Bulovic et al. [38], fabricated a device in which Mg/Ag was the bottom contact and ITO the top electrode. The advantage of this type of architecture is that it allows for easier integration with n-type TFTs (see Section 7.5 for a discussion of active-matrix drive OLED displays). 

Fig. 5 /d-Tds characteristics for polydiacetylene monolayers, assembled and polymerized on the air-water interface (inset) and transferred to form bottom-contact, bottom-gate p-type FETs... 

In order to examine the contact effects on both yUi and jj,2, TOF was carried out on similar samples with different top and bottom contacts (gold, aluminum, copper, and Sn02). From the results, it can be concluded that both fix and 2 are independent of the top and bottom contact and also of the apphed field. These observations indicate... 

During main drying, the situation is very different the condition of a close contact with the product is only true at the beginning of MD thereafter, the measured temperature depends on circumstances which are difficult to analyze. The position of the sensor, on top, in the center or near the bottom contact with the vial wall, decides the measured data, as shown in Figure 1.76. If the filling volume of vials is small (a few millimeters layer thickness) or if the product is granular, it is especially difficult to ob-... 

OFETs with wet-deposited films of 48 as the active layer in bottom contact geometry were fabricated on highly doped n-type silicon wafers with the organic semiconductor layer (ca. 50 nm) deposited from chloroform solution [70], OFETs made from 48 exhibited negative amplification, which is typical of... 

Fig. 1.3. Schematic view of the structure of organic thin film transistors. Both structures are top-gated, (a) Bottom contact (BC) (b) Top contact (TC).

In addition to improving structural order, reliable improvements of device performance have been demonstrated through optimization of device interfaces and architectures. The architectures are perhaps more easily addressed, and are also related to improving the structural order. Several possible constructions of TFT are known from the long history of silicon-based devices. These were the first architectures adopted for OTFTs also. Top and bottom contact, indicating the location of the source and drain electrodes with regard to the semiconductor, are the most widely used. 

The performance of bottom-contact devices, fairly easy to fabricate with traditional lithographic equipment, can also be improved by control of the interface where the metal source and drain layers make contact with the semiconductor. 

Fig. 2.4. The often dramatic effects bottom contacts can have on molecular ordering in organic semiconductors like pentacene. A. Schematic diagram of the type of disorder introduced in pentacene s lamellar structure as thin-film growth encounters a step, for example...

Bottom-gate, top-contact (Fig. 4.2a) and a bottom-gate, bottom-contact (Fig. 4.2b) TFT configurations are used to evaluate the FET performance of our semiconductors. The devices are built on an n-doped silicon wafer (gate electrode) with a 100-nm thermal silicon oxide (SiC>2) dielectric layer which is modified with a self-assembled monolayer of octyltrichlorosilane (OTS-8) to promote molecular ordering in the semiconductor layer. For the top-contact device the semiconductor layer ( 20-50 nm) is deposited on the OTS-8-modified SiC>2 surface by spin coating. A... 

Fig. 4.2. Schematic diagrams of bottom-gate, top-contact (a) and bottom-gate, bottom-contact (b) thin film transistor test configurations.

Fig. 15.9. Bottom-contact pentacene TFT characteristics before and after parylene passivation. The device has W/L = 400/80 pm. The passivation degrades the mobility whereas the threshold potential is relatively steady.

A 0.5-pm film of parylene-C was deposited on pentacene TFTs at room temperature. TFT characteristics were measured and compared before and after the deposition without patterning of the parylene. The bottom-contact TFT (W/L = 400/80 pm) characteristics before and after parylene passivation are compared in Fig. 15.9. Field-effect mobility decreased by 50% from 1.6 cm2 V-1 s-1 to 0.80 cm2 V 1 s 1 whereas the threshold voltage stays the same. 

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