transfer printing techniques for flexible and stretchable inorganic electronics - heat transfer printing film
Transfer printing technology is a new deterministic micro-assembly technology.
Manufacturing and Nano
Manufacturing, which enables heterogeneous integration of material types into the required functional layout.
It creates engineering opportunities in the field of flexible and stretchable inorganic electronics with the same performance as conventional wafers
Based on the device, but able to deform like rubber, in which prefabricated inorganic semiconductor materials or devices that need to be transferred to the bulk wafer-
Printed on unconventional flexible substrates.
This paper briefly reviews the latest developments in transfer printing technology for flexible stretchable inorganic electronic devices.
The basic concepts of various transfer printing technologies are outlined.
The performance of these transfer printing technologies was summarized and compared, and then the prospects and challenges for future development and application were discussed.
The past decade has witnessed the rapid progress and great achievements of flexible and stretchable inorganic electrons, it eliminates plane, rigidity, brittle design constraints associated with conventional electrons by integrating hard inorganic semiconductor materials into fine structural layouts with flexible substrates.
This technology makes it possible for many new applications that cannot be realized by traditional electronic products, such as curve electronic products, bio-electronic products, etc.
Integrated Electronics, skin electronics, transient electronics, deformed optoelectronic
Electronic products and many other products.
The figure shows some examples of flexible and stretchable inorganic devices whose performance is equal to the use of well-
Inorganic semiconductor and metal materials have been developed, but in a foldable, pulable and curved format.
These examples include Si-that can be pulled out and folded-CMOS circuit (Fig. )
Curve electronics (
Semi-spherical electronic eye camera in figure 1), bio-
Integrated Electronics (
Figure 1. multi-functional medical balloon catheter
And ultra-thin shape-preserving creatures
Integrated neural electrode array in Fig. )
Electronic skin (Fig. )
Transient electrons (Fig. )
Deformed photoelectricelectronics (
Flexible photovoltaic modules in figure 1
A highly stretchable AlInGaP μ-
The ILEDs array in the figure
Figure 1 mechanical curved array of ultra-thin, micro, blue LEDs).
All examples in the figure
Inorganic semiconductors or metal materials need to be integrated with flexible polymer substrates.
However, inorganic semiconductors or metal materials cannot be manufactured directly on flexible polymer substrates using traditional manufacturing techniques because flexible polymer substrates cannot withstand extreme processing conditions such as high temperature or chemical etching.
The manufacturing process of a flexible electronic system begins when the device is manufactured independently on a wafer/donor substrate, and then the device is assembled onto a flexible/stretchable substrate.
Transfer printing technology enables solid objects to transfer from the donor substrate to the receiver substrate in a high yield manner, providing the most promising solution for this assembly process.
This method separates the manufacturing substrate from the application substrate, bypassing the compatibility problem of the polymer substrate with the traditional manufacturing technology with a mature and mature commercial infrastructure, thus speeding up the commercial of flexible tensile inorganic electronic products.
Example in figure
Demonstrates the extraordinary ability of transfer printing technology to assemble countless materials with certainty (
Also known as ink)
Flexible stretchable inorganic electronic products that form spatial organization and functional arrangement on various substrates.
Inks for flexible and stretchable inorganic electrons in transfer printing include hard inorganic materials (e. g.
Inorganic semiconductors and metals)
Integrated inorganic devices (e. g.
Inorganic thin film transistor
Interim term contract, inorganic LEDs-
ILEDs and solar cells)
Fully integrated inorganic circuit.
It should be noted that the ink for transfer printing is not limited to inorganic materials, but also other materials such as carbon materials (e. g. , graphene)
Organic materials (e. g.
Organic Semiconductor)and cell-sheet-
Integrated equipment for flexible bio-electronics.
With regard to transfer printing technology, there are currently several comments on materials and applications.
This paper reviews the progress of transfer printing technology for flexible tensile inorganic electrons (i. e.
Transfer printing technology for inorganic semiconductor and metal materials, devices and circuits)
From the perspective of methodology
The basic principles of transfer printing technology are first introduced, and then various transfer printing technologies are outlined.
According to the basic concept and working principle of pad printing technology, they are classified and briefly summarized.
Finally, the performance of transfer printing technology is compared, and some prospects and challenges are put forward for the future development and application.
The most general form of the transfer printing process is the use of soft elastic stamps to adjust the physical mass transfer of the micro-device (
Usually called Ink)
As shown in the figure, between the donor substrate and the secondary receiver substrate.
It usually consists of two steps: Retrieval/picking
Ink up from the donor base and printing/delivering the ink to the receiver base.
At the beginning of the retrieval process, the stamp is in contact with the donor substrate, on which the ink is usually prepared in an orderly and releasable manner by wet chemical etching or dry etching (e. g. , laser lift-off).
For example, wet chemical etching produces releasable ink by etching the sacrifice layer between the ink and the substrate, but has an appropriately defined anchor structure to retain the print-defined spatial layout of the elements.
Proper pre-loading is applied on the stamp to ensure a shape-preserving contact between the stamp and the ink, which provides sufficient adhesion to retrieve the ink from the donor substrate.
The retrieval process can be
Selectivity in a large scale parallel manner for high throughput or selective precise operation of a single ink or multiple inks.
The ink seal is then in contact with the receiver substrate, and then the printed ink that the modulation seal/ink adheres to the receiver substrate.
The removal of stamps completes the transfer printing process.
Print mode can also be right
Selective or selective
Basic physics related to the transfer printing process falls within the scope of fracture mechanics, which involves a three-tier system (
There are two interfaces (
Stamp/ink and ink/substrate interface)
As shown in the figure. .
The competitive break between the stamp/ink interface and the ink/substrate interface determines whether retrieval or printing occurs.
During the retrieval process, the seal/ink interface should be stronger than the ink/substrate interface so that the ink can be retrieved through the seal.
During printing, the stamp/ink interface should be weaker than the ink/substrate interface so that the ink can be released from the stamp.
The output of transfer printing depends on the ability to switch bonding between the strong and weak states of retrieval and printing, respectively.
Usually, the adhesive strength on the interface of the ink/substrate has nothing to do with external stimuli and is considered constant.
Therefore, the key to successful transfer printing is the adhesion modulation of the stamp/ink interface.
The diagram illustrates the basic principles of transfer printing technology: retrieval in a strong stamp/ink adhesion state, printing in a weak stamp/ink adhesion state, adhesive strength of the ink/substrate interface (red solid line)
When the adhesive strength on the stamp/ink interface remains the same (
Black solid line)
It is modulated by external stimuli such as stripping speed and lateral movement.
Adhesion switchability is defined as the ratio of the maximum adhesive strength to the minimum adhesive strength, which can be used to evaluate the adhesion adjustment performance.
Based on the principle of adhesive modulation of stamp/ink interface, transfer printing technology is divided into surface chemistry and glue assisted transfer printing technology, motion control transfer printing technology, laser-driven non-
Gecko-contact transfer printing technology
Transfer of inspiration printing technology (
Represents a set of techniques that have a fiber surface assisted by specific operations such as retraction angle or lateral movement, and aphid-
Transfer of inspiration printing technology (
Represents a set of technologies based on changes in contact area).
To improve the reliability of the retrieval and printing process, surface chemical modification or glue is used to adjust the adhesive strength of the interface.
The figure shows a typical surface chemistry and glue assisted transfer printing process, which was retrieved with the aid of surface chemistry and glue assisted printing.
The strong seal/ink adhesion required for retrieval is condensation achieved by a slightly oxidized silicone rubber seal surface and a Si-O-Si chemical binding between the fresh SiO film coated on the target ink reaction.
Printing is achieved by coating a thin layer of glue that is usually in a liquid/uncured state, partially cured state to increase the adhesion of the ink/substrate interface, or a low modulus curing state.
Uncured or partially cured glue is further cured by heating or exposure to UV to enhance the adhesion between the ink and the receiver substrate.
Although surface chemistry and glue can enhance the reliability of retrieval and printing, the density of chemical bonds must be carefully designed in order to successfully remove ink from stamps.
Moreover, additional SiO layers are required to enhance the adhesion of the stamp/ink to complicate the process, and may cause stamps of stamps because of the chemical reaction of the SiO layer and the contamination of the glue after transfer printing.
The surface treatment of the donor substrate is also a key factor in the transfer printing process.
Some materials have strong adhesion to the donor substrate, so proper surface treatment should be carried out, such as self-
A single layer that needs to be assembled to weaken the adhesion between the ink and the donor substrate.
For example, in the case of colloidal quantum dot transfer printing, the interaction between nanoparticles and substrates should be within the appropriate range of effective transfer printing and specific surface treatment (e. g.
, 18 Poly three metho self-silicon coating
Assembling single molecular film
It is usually required before coating the nanoparticles solution on the donor substrate.
Another transfer printing technology involving surface chemistry is tape transfer printing, where solvent-releasable tapes or heat-releasable tapes are used as stamps. Figures b-
1 demonstrated a typical transfer printing process based on commercial solvent releasable tape to retrieve and print equipment with high yield.
The high adhesive strength between the tape and the ink ensures the high reliability of retrieving the ink from the donor substrate.
During the printing process, the introduction of the solvent significantly reduces the adhesive strength of the stamp/ink interface by decomposing the interface and even the entire tape, almost zero, this ensures that the ink is printed to the receiver substrate with high reliability. Figures b-
2 shows the adhesive strength of 3 m 3850 tape on glass before and after the introduction of acetone, which clearly shows the effectiveness of adjusting the adhesive strength by surface chemistry.
Although tape transfer printing provides a simple but highly reliable method for Heterogeneous Integration of materials, it usually leaves a certain residue on the ink, which may reduce the performance of the equipment.
The figure shows some equipment supported by surface chemistry and glue assisted transfer printing technology :(1)
A high-performance thin film transistor constructed on a photosensitive epoxy coated PET substrate ,(2)
3D silicon n-array
Channel metal oxide semiconductor inverters on polymer acid coated PI substrate, and (3)
EMG sensors mounted on the skin of the forearm.
Although surface chemistry and glue-assisted transfer printing techniques are simple and clear, they have inherent limitations such as surface contamination, which may lead to frequent replacement of stamps and may reduce equipment performance.
To overcome these limitations, advanced transfer printing techniques based on adjustable homophonic and reversible dry adhesion have been developed and will be discussed in the following sections.
A powerful multi-function transfer printing technology, dynamic control transfer printing technology, using the speed
The dependency adhesion effect of the sticky stamp to retrieve the ink from the donor substrate at a high speed (
~ 10mm/s or more)
And print the ink to the receiver substrate at low speed (