Intrinsic nonuniformity in the polycrystalline-silicon backplane transistors of active matrix organic light-emitting diode displays severely limits display size. Organic semiconductors might provide an alternative, but their mobility remains too low to be useful in the conventional thin-film transistor design. Here we demonstrate an organic channel light-emitting transistor operating at low voltage, with low power dissipation, and high aperture ratio, in the three primary colors. The high level of performance is enabled by a single-wall carbon nanotube network source electrode that permits integration of the drive transistor and the light emitter into an efficient single stacked device. The performance demonstrated is comparable to that of polycrystalline-silicon backplane transistor-driven display pixels.
We present the first display panels exploiting the nVerPix CN- VOLET technology that reduces the pixel circuit of the conventional AMOLED display to two discrete components: the switching transistor and the CN-VOLET. This permits high aperture ratio bottom emission displays—as high as 70% here— and greatly simplifies the manufacturing. Mono-color QVGA AMOLED displays (6.4 cm diagonal) playing video will be shown.
A new architecture light emitting transistor combining the drive transistor, storage capacitor and light emitter into a single device promises to greatly reduce AMOLED manufacturing costs by dramatically reducing the backplane circuit complexity. Here we demonstrate device operation at 60 Hz using only a switching transistor and show remarkable stability under bias stress, despite use of an organic channel.
An improved process for graphene transfer was used to demonstrate high performance graphene enabled vertical organic field effect transistors (G-VFETs). The process reduces disorder and eliminates the polymeric residue that typically plagues transferred films. The method also allows for purposely creating pores in the graphene of a controlled areal density. Transconductance observed in G-VFETs fabricated with a continuous (pore-free) graphene source electrode is attributed to modulation of the contact barrier height between the graphene and organic semiconductor due to a gate field induced Fermi level shift in the low density of electronic-states graphene electrode. Pores introduced in the graphene source electrode are shown to boost the G-VFET performance, which scales with the areal pore density taking advantage of both barrier height lowering and tunnel barrier thinning. Devices with areal pore densities of 20% exhibit on/off ratios and output current densities exceeding 106 and 200 mA/cm2, respectively, at drain voltages below 5 V.
In contrast to typical metals, carbon nanotubes are shown to form a unique Schottky barrier contact with semiconductors wherein a gate field can modulate not only the band bending in the semiconductor but also the height of the barrier. These phenomena are exploited to enable two new device architectures: a vertical field-effect transistor (figure) and a vertical light-emitting transistor.
State-of-the-art performance is demonstrated from a carbon nanotube enabled vertical field effect transistor using an organic channel material. The device exhibits an on/off current ratio >105 for a gate voltage range of 4 V with a current density output exceeding 50 mA/cm2. The architecture enables submicrometer channel lengths while avoiding high-resolution patterning. The ability to drive high currents and inexpensive fabrication may provide the solution for the so-called OLED backplane problem.
The large current densities attained by carbon nanotube enabled vertical field effect transistors using crystalline organic channel materials are somewhat unexpected given the known large anisotropy in the mobility of crystalline organics and their conventional ordering on dielectric surfaces which tends to orient their high mobility axes parallel to the surface. This seeming contradiction is resolved by the finding that the nanotubes induce a molecular ordering that reorients the high mobility axes to favor current flow in a direction perpendicular to the substrate surface.