Active Matrix Array Device With Thin Film Heater
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Solution Overview
Problem
Current heat treatment methods for forming polycrystalline silicon thin-film transistors on glass substrates are limited by the degradation of glass substrates at high temperatures and the inability to achieve uniform grain structure and device characteristics, particularly in mass production, due to the sensitivity of laser-based methods and metal contamination in metal-induced crystallization processes.
Innovation Solution
Integration of a thin film conductive heater element arrangement beneath the semiconductor layers, allowing for localized heating during crystallization and dopant activation, which simplifies manufacturing and extends the device's operational lifetime by maintaining the heaters within the device structure, enabling low-temperature processing and reducing substrate damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If solid phase crystallization is used to crystallize amorphous silicon, then the semiconductor layer can be formed, but the glass substrate is damaged due to high temperatures
Solution Approach 1:
The patent segments the heating function by introducing a separate heater layer (e.g., Mo, W, or doped polysilicon) deposited on the glass substrate. This heater layer is patterned to correspond to the semiconductor layer regions, allowing localized heating without heating the entire substrate to damaging temperatures. The heater acts as an independent thermal management component that enables high-temperature crystallization processes while protecting the glass substrate from thermal damage.
Solution Approach 2:
The heater layer serves as an intermediary thermal management component between the power supply and the semiconductor layer. It converts electrical energy to localized thermal energy directly at the semiconductor interface, enabling precise temperature control during crystallization. This intermediary structure allows the system to achieve the required crystallization temperatures (500-600°C) without exposing the glass substrate to equivalent thermal stress.
2Temperature
If excimer laser crystallization is used, then lower temperatures can be achieved, but uniform grain structure and device characteristics cannot be achieved due to sensitivity to beam energy
Solution Approach 1:
The heater layer is self-patterned through photolithography and etching processes that are already part of the standard TFT fabrication sequence. The heater pattern automatically aligns with the semiconductor layer regions, eliminating the need for separate alignment procedures. This self-service approach ensures consistent heating zones across all devices, leading to uniform grain structures and reproducible device characteristics without the sensitivity issues associated with laser beam positioning.
Solution Approach 2:
The patent replaces the mechanical/optical laser beam system with an electrical heating system. Instead of using a moving laser beam that requires precise positioning and energy control, the heater layer provides uniform thermal energy through electrical resistance heating. This substitution eliminates the sensitivity to beam energy variations and positioning errors, achieving consistent crystallization results across large substrate areas.
3Temperature
If metal induced crystallization is used, then crystallization can occur at low temperatures, but metal contamination causes detrimental leakage current
Solution Approach 1:
The patent changes the material parameter of the heater layer from metal to metal-compatible materials such as molybdenum, tungsten, or doped polysilicon. These materials can be deposited at low temperatures using sputtering or CVD techniques and provide sufficient resistive heating for crystallization. By selecting materials that do not diffuse into the semiconductor layer, the process achieves low-temperature crystallization without introducing harmful metal contamination that would cause leakage currents.
Solution Approach 2:
The patent employs composite material structures where the heater layer is deposited as a separate functional layer distinct from the semiconductor and dielectric layers. This layered composite structure allows each material to perform its specific function: the heater layer provides thermal energy for crystallization while being electrically isolated from the semiconductor channel, preventing contamination. The composite approach enables low-temperature processing without the harmful effects of metal diffusion.
4Loss of time
If rapid thermal anneal with optical heating source is used for dopant activation, then short duration heating is achieved, but excessive heating of the glass substrate occurs
Solution Approach 1:
The heater layer is patterned with local quality variations to provide differentiated thermal management. Regions under the source and drain contacts have higher heater resistance for rapid dopant activation, while regions under the channel have lower resistance to prevent excessive heating. This spatially varying heater design enables short-duration annealing for dopant activation without causing excessive substrate temperature rise that would damage the glass or affect liquid crystal materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the formation of high-quality polycrystalline silicon thin-film transistors with improved uniformity and reduced metal contamination, extending the operational range and lifetime of the devices while avoiding the need for expensive laser processing and minimizing substrate damage.
Implementation Method 1
a thin film conductive heater element arrangement provided over the substrate
Implementation Method 2
heating the semiconductor layer to crystallize at least portions of the layer to form polycrystalline silicon
Data Source
AI summary
An active matrix device has an array (54) of device elements, each of which comprises at least one thin film transistor (34). A thin film conductive heater element arrangement (10) is provided over a substrate of the device, and the semiconductor islands of the thin film transistors are provided over the heater element arrangement (10). The heating arrangement can remain in place in the device, thereby avoiding the need to remove the layers of the heater element arrangement during processing.