Lipu Zhou

We have fabricated organic thin-film transistor (OTFT)-driven active matrix liquid crystal displays on flexible polymeric substrates. These small displays have 16×16 pixel polymer-dispersed liquid crystal arrays addressed by pentacene active layer OTFTs. The displays were fabricated using a low-temperature process (<110 °C) on flexible polyethylene naphthalate film and are operated as reflective active matrix displays.

We report on parasitic contact effects in organic thin film transistors (OTFTs) fabricated with pentacene films. The influence on the OTFT performance of the source and drain contact metal and the device design was investigated. Top contact (TC) and bottom contact (BC) gated transmission line model (gated-TLM) test structures were used to extract the combined parasitic contact resistance as a function of gate voltage swing and drain-source voltage for OTFTs with gold source and drain contacts. For comparison BC test structures with palladium contacts were studied. Differences in the bias dependence of the contact resistance for TC and BC OTFTs indicate that charge injection and device performance are strongly affected by the device design and processing. The results from this investigation show that TC and BC device performances may be contact limited for high mobility OTFTs with channel lengths less than 10μm.

In this paper, we address the problem of extrinsic calibration of a camera and a 3D Light Detection and Ranging (LiDAR) sensor using a checkerboard. Unlike previous works which require at least three checkerboard poses, our algorithm reduces the minimal number of poses to one by combining 3D line and plane correspondences. Besides, we prove that parallel planar targets with parallel boundaries provide the same constraints in our algorithm. This allows us to place the checkerboard close to the LiDAR so that the laser points better approximate the target boundary without loss of generality. Moreover, we present an algorithm to estimate the similarity transformation between the LiDAR and the camera for the applications where only the correspondences between laser points and pixels are concerned. Using a similarity transformation can simplify the calibration process since the physical size of the checkerboard is not needed. Meanwhile, estimating the scale can yield a more accurate result due to the inevitable measurement errors of the checkerboard size and the LiDAR intrinsic scale factor that transforms the LiDAR measurement to the metric measurement. Our algorithm is validated through simulations and experiments. Compared to the plane-only algorithms, our algorithm can obtain more accurate result by fewer number of poses. This is beneficial to the large-scale commercial application.

We report on organic thin-film transistors fabricated using the small-molecule organic semiconductor naphthacene as the active layer material with device performance suitable for several large-area or low-cost electronics applications. We investigated naphthacene thin films deposited by thermal evaporation onto amorphous substrates held near room temperature. Using atomic-force microscopy and x-ray diffraction we find naphthacene films consist of a high density of submicron-sized grains with a surprisingly high degree of molecular order. Thin-film transistors fabricated using evaporated naphthacene films on thermally oxidized silicon substrates have field-effect mobility larger than 0.1 cm2/V s, current on/off ratio greater than 106, negative threshold voltage, and subthreshold slope of 1 V/decade.

We use grazing incidence x-ray scattering to study the molecular structure and morphology of thin (70 ML) crystalline films of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Au(111) surfaces as a function of film thickness, substrate temperature, and growth rate. Although the first two PTCDA monolayers grow in a layer-by-layer fashion, the film evolution beyond the second monolayer depends strongly upon the growth conditions resulting in low-temperature [i.e., nonequilibrium (NEQ)] and high-temperature [equilibrium (EQ)] growth regimes. In the NEQ regime, the films roughen monotonically with increasing film thickness, but retain a well-defined film thickness. Furthermore, we find that these films have a lattice strain which is independent of film thickness. In the EQ regime, the film acquires a three-dimensional morphology for thicknesses >2 ML, and the lattice strain decreases rapidly with increasing thickness. We also show that the transition between the NEQ and EQ regimes is sharp and depends upon the balance between the growth rate and substrate temperature. These results suggest that the PTCDA/Au(111) system is thermodynamically described by incomplete wetting, and that strain and kinetics play an important role in determining molecular organic film characteristics.