fully automated 3d printing of Rigid-Flex structures with distributed electronics

This is first-of-its-kind work demonstrating fabrication of 3D structures containing active electronics of many layers with micron-scale resolutions -- performed with complete automation from start to finish, inside an inkjet-3D printer. [ No intermediate steps that need a human or robot in-loop, no post-processing requirements, no usage of external tools ]

I have achieved high complexity in part fabrication with rapid customization capabilities, producing both active and passive components including low-level computational elements. This approach offers unmatched automation and design flexibility that surpasses latest industry and academic standards.

I independently conducted all aspects of this research, including materials formulations, process development, part design, extensive characterization of 1000's of devices. (With invaluable inputs from my PhD advisor Prof. Rob MacCurdy).

A rigid-flex PCB fabricated in one-step without requiring cutting, bonding, silk-screens, masks etc. It has both flexible regions that can be rolled up, and rigid regions to hold components securely

Heterogeneous Integration: one-step inkjet fabrication of a flex pcb with selectively-rigid regions to hold externally-placed components securely

Simultaneously deposits two different UV-curing dielectrics which are rigid and soft in different regions in one step, without traditional cutting-bonding steps. It is directly printed on a glass or silicone mat, and easy to release.
Conductive materials are printed on this rigid-flex layer, with the bed maintained at 80C temperature to sinter the highly-conductive silver ink.
This process can be repeated across many layers to build it into 3D.
The rigid-regions gently transition into the flexible regions with a buffer zone comprised of digital-mixtures of rigid and flexible material that is created in-situ while printing. This ensures that there are no points of high-stress which can crack the structure. This is a capability is not directly possible to achieve with other fabrication methods.

Version 1: LED-flashing circuit with a 555-timer IC, resistors and a capacitor. Components were reflow-soldered on the inkjet-printed PCB

Version 2: LED-flashing circuit - but with two resistors and a capacitor Printed-in-Place simultaneously while depositing the conductive silver traces. Only the 555-timer IC and LED were soldered

3D-circuits with via-free interconnects across multiple layers

This is a version of a simple LED-Flashing circuit converted into a multi-layer design to save space. Does not require traditional vias between layers
Each sample shown here has resistors printed-in-place on the bottom layer of different values. All 3 samples were fabricated simultaneously

3D Laser Microscope Scan of an automatically-printed 3D-circuit with multiple layers connected without requiring traditional vias

Thin-film printed transistor using organic semiconductors and a solid-state electrolyte, which is functional-as-printed

They show I-V characteristics similar to a traditional transistor. They can be cascaded to form more complex computational elements, sensors / transducers for multi-modal stimuli, and amplifiers

3D-printed Active Electronics

Active Electronic devices are those which change their behavior or properties under an electronic input or other stimulus (unlike resistors and capacitors which have fixed values)

Here, I demonstrate fully-inkjet printed Organic Electrochemical Transistors (OECT)

These are 3-terminal devices comprising of a semiconducting channel with Drain and Source, and a Gate to modulate the channel behavior. Instead of using an Electric Field like a FET, this uses an ionic material between the Gate and Channel to modulate the doping level of the channel to control the behavior
All materials are solution-processable and printable below 90C temperature. These devices have high-degree of design freedom to work as sensors of many types and as neuromorphic-computation elements

Schematic showing the many different material layers forming a single OECT device. These materials are deposited either simultaneously or sequentially during fabrication to form devices that are functional-as-printed

Simple stack of two individual transistors printed on top of each other, but electrically isolated.

Since every material is printed and encapsulated, we can progress towards building more layers of devices in 3D, without requiring lamination or other intermediary steps

Multi-Layer Stacks and Cascading of transistors to form complex devices

with via-free interconnects spanning 4-layers of devices

Cascading multiple printed-transistors to form logic-gates. Shown here is data collected from a functional NAND gate