Vertical Thin-Film Transistor Structure for Short-Channel Display Panels

The patent transitions from a planar channel structure to a vertical channel structure by forming protrusions on the substrate. The channel portion is positioned on the side surface of the protrusion, creating a three-dimensional configuration. This dimensional change allows the channel length to be defined by the height of the protrusion rather than the lateral distance between source and drain electrodes, enabling shorter effective channel lengths while maintaining easier manufacturing control through vertical etching processes.

The protrusion is divided into multiple sub-protrusions (first sub-protrusion and second sub-protrusion) with different materials and etch resistances. This segmentation allows for precise control of the channel length by using the second sub-protrusion as a mask during etching of the first sub-protrusion. The channel length is determined by the height difference between sub-protrusions, enabling precise control without requiring high-precision lateral patterning.

By moving the channel to a vertical orientation on the protrusion side surface, the transistor footprint on the substrate is dramatically reduced while maintaining adequate channel length for reliable operation. The volume reduction comes from eliminating large lateral spacing requirements, yet the vertical channel provides sufficient length for carrier transport, maintaining reliability despite compact packaging.

The protrusion uses composite materials with different etch resistances (oxide material for first sub-protrusion, nitride material for second sub-protrusion). This composite structure provides built-in process control where the differential etching rates create self-aligned features, reducing process variation impact and improving device-to-device consistency even in high-density configurations.

The vertical channel configuration decouples the channel length from the lateral dimensions that are difficult to control precisely. The channel length is now determined by vertical film thicknesses and etch depths, which can be controlled with higher precision using standard semiconductor fabrication processes. This enables shorter effective channel lengths for higher frequency operation without the same level of lateral patterning precision requirements.

The second sub-protrusion is formed first as a mask structure, establishing the precise channel length boundary before the channel-forming etch is applied. This preliminary formation of the masking structure ensures that the channel length is predetermined by the second sub-protrusion height, and subsequent processing steps automatically inherit this precision without requiring additional high-precision alignment operations.

While the transistor structure is segmented into multiple sub-protrusions, each segment serves a single, well-defined function: the first sub-protrusion provides the channel formation region and the second sub-protrusion provides the length-control mask. This functional segmentation, while increasing structural elements, actually simplifies the processing sequence by using self-aligned steps where each layer automatically defines the next, reducing the need for complex alignment procedures that would otherwise increase overall device complexity.

The second sub-protrusion is positioned on top of the first sub-protrusion, creating a nested configuration where the taller second structure contains the shorter first structure within its lateral footprint. This nesting allows the channel length to be defined by the vertical profile of the nested structures, enabling precise control while minimizing the lateral space required, thus achieving high integration density without proportionally increasing processing complexity.