Frequently Asked Questions
HETEROMERGE offers complete multi-material solutions for 3D printing of functional microsystems. We rely on 2-photon-polymerization based 3D laser direct writing. This is one of the finest and at the same time fastest 3D printing processes today. In this section, we answer frequently asked questions about our currently available MergeOne add-on and our multi-material technology for two-photon polymerization (2PP) systems.
Questions about the product
We do not sell 2PP printers but instead upgrade existing 2PP printers with our print head technology to enable them to perform multi-material 3D printing with smallest line width (below 200 nm) and highest material placement accuracy (below 50 nm lateral). At the moment, the system is sold as add-on to existing 2PP systems.
Currently, our MergeOne system is available for Nanoscribe Photonic Professional GT+ and GT2 systems. For Nanoscribe Photonic Professional GT systems, an installation is also possible, but with some restrictions in handling. Our system offers appropriate interfaces for automating the printing and material exchange process. The MergeOne system is currently also available for customized (“self-builds”) with limitations in handling and requires using third-party software. We plan to offer an API (application programming interface) for such custom builds in the future to enable automated multi-material printing with them as well.
Besides a 2PP system, pressurized air or nitrogen and vacuum is required. Basically, the system can operate with an pressure up to 8 bar. If the pressure is lower than 8 bar, the system can work with it but will not be able to provide its maximum output. That means, for some very viscous materials the process exchange time might be increased. For example, for about 30-50 Pas viscosities we usually operate at about 6 bar. Our system accepts 6 mm outer diameter rigid and flexible tubing. The vacuum is required to remove material from the print region via something like a bubble trap. That means under correct handling circumstances there should be no liquid going from the bubble trap into our control system, and thus also, not further down the vacuum line. However, it cannot be excluded that low volatile compounds (monomers evaporated) will be pumped as gaseous phase via our system down the vacuum line. So far, we did not observe any impact on our system and the vacuum line after long operation. Of course, in case of wrong operation, there can be liquid transported further into our system and as a consequence further down the vacuum line. In this case, our control system will be at risk for damage and would need to be refurbished.
Which capabilities do you lose when you use MergeOne? Will the functionality of the printer be limited?
No. The MergeOne system is designed for maximum compatibility with and easy integration into existing 2PP systems and the usual 2PP workflow. In principle, most of the MergeOne components can remain in the 2PP printer without restricting a normal printing process.
No. The MergeOne system has no influence on the working distance. All 2PP prints with our MergeOne system can be performed as if the MergeOne system was not integrated. This means that all print files that have been developed independently of the MergeOne system can continue to be used.
For the mentioned systems of the company Nanoscribe we offer a software automation. The entire printing process as well as the material change is controlled by our software SCULPTOR. This software communicates with NanoWrite for this purpose. The user only has to start NanoWrite and make a simple one-time initialization, which will only remain in effect for the printing session. At the end of the printing session, the system is automatically restored to its default state and is available for normal use. No long lasting change is made to the system.
No. No changes are made to the original configuration of the system. If the SCULPTOR software is not executed, the system is in its factory state or in its functional state previously adapted by the customer. This concerns especially all definitions of objective positions to provide maximum user comfort and safety.
The setup takes about 30-45 min for an inexperienced user. Experienced users can reduce this time to below 30 min.
How long does the dismantling take? How often does the print head system need to be cleaned? How does it work? How long does it take?
The dismantling of the print head, including cleaning, takes about as long as the setup. Cleaning essentially involves flushing the fluidic components, usually with isopropanol and nitrogen or compressed air. Only simple manual operations by the user are required here. Cleaning is the main part of the dismantling process and can be carried out by experienced users in less than 30 minutes. If the MergeOne system is used intensively, we recommend cleaning after approx. 1 week of use or as soon as a long print job with this duration has been completed.
MergeOne does not permanently interfere with the printer system. Therefore, damage is very unlikely if used properly. Should damage nevertheless occur to the 2PP system, which can be proven to be due to incorrect functioning of MergeOne, we will be liable for the proven damage. The customer is responsible for proper application. For damages caused by improper use by the customer, we cannot assume liability. Further details can also be found in our GTCs.
While the open fluidic solution has some challenges regarding process control it offers huge advantages in terms of the print height being not limited by flow cell size, the accessible print area being only dependent on the chosen substrate, and the capability of the printer as well as being able to easily print onto a large variety of form factors of substrates including active optoelectronic devices.
As mentiond before, there is no invasive modification of the 2PP system we upgrade. That means normal 2PP printing and usage of the printer is not impacted at all.
We do not use pumps for our system. We use lab-supplied pressurized gas (preferred nitrogen) and vacuum along with pressure regulators to create drive our system. If preferred by the customer, stan along compressors and pumps can be used to provide pressure and vacuum. We recommend placing them at a sufficient distance from the printing tool if needed.
Questions about material exchange
The exchange time depends on the viscosity of the print material and the geometric complexity of the print object. For materials with low viscosity, the exchange time is usually less than 5 min. As the viscosity increases, the exchange time also increases, so that for materials with medium and very high viscosity, it is between 5 min and 50 min. The highest viscosity we have tested so far is beyond 30 mPas.
The dead volume of the current fluidic system is about 300-400 µL. 50-100 µL of volume is usually required per exchange.
So far, we have not been able to detect any damage to typical print structures even with larger aspect ratios. Due to geometric conditions, the material exchange takes place by a highly laminar flow. The flow velocity is about 50 µm/s for a typical process. This is below the typical flow velocity that occurs when the objective is moved away from the printing region.
Currently, the exchange is based on proven and defined recipes. They are supplied by HETEROMERGE for standard materials for the respective standard configuration purchased by the customer. The customer can create his own exchange recipes as desired.
The exchange can be monitored by the customer with the help of an additional camera provided by HETEROMERGE. There is the possibility for the customer to intervene in the exchange process if desired. In addition to the variation of process parameters, an exchange in a so called “manual mode” can be repeated until the complete material exchange has taken place. This has been proven to be very useful especially for new structures and the development of new customer-specific material exchange recipes.
In the printing area, the material is completely replaced. Only in the peripheral area of the exchange droplet do small residual amounts of the pre-material remain. This is completely uncritical, as the respective area is far away from the printing region.
MergeOne only works with the so called dip-in mode, i.e., in immersion of the lens with the print material.
Residual material should remain in the material reservoirs. The provide small volume bottles are UV-tight and can be stored according to the manufacturer’s recommended storage conditions for the printing materials being used. Other fluidic components should be cleaned regularly after use.
Does flushing have to be carried out during exchange? Would it not be useful so that minimal residual material remains during each exchange process?
The material exchange takes place without a cleaning or rinsing process. Excessive non-cured material is only removed in post-processing after the entire printing process has been completed. Flushing of the fluidic components can then take place separately and independently of the printing process.
We use reservoirs filled at maximum with 10 ml printing material at the moment for process and user convenience minimizing refill steps. The current system can be operated with as low as 2 ml filling of the reservoir. We have an experimental procedure that can work with less than 1 ml of printing material. We are also working on reservoirs with about 1 ml capacity for applications where small volumes are relevant. The consumption was discussed in a separate question.
Which materials can be printed or are suitable for multi-material printing? Can metals or glass also be printed?
Any materials that can be used must have a liquid to pasty state (viscosity between 500 mPas and 50 Pas). Current materials are usually based on an organic matrix. These typical 2PP materials are further usually based on free radical polymerizing monomer systems, such as acrylates or hydrogels. All commercially available materials for 2PP can also be used with MergeOne. Metals and glasses can be integrated into the base matrix via functional additives. Here, it may be necessary to ensure that all materials are compatible for post-processing steps.
The typical viscosities for which recipes are available are between 500 mPas and 50 Pas.
General questions about the printing
Currently, the MergeOne system is available for 25x objectives from ZEISS. With this, writing fields up to 400 µm are possible. Larger structures are assembled using the respective concepts offered by the printer (stitching). Prints with heights up to the millimeter range are possible. The smallest structures are in the range of 1 µm due to the used objective. Smaller and larger structures will be available in perspective with new print heads as suitable objective adapters.
Yes, this is possible. However, stitching is necessary for lateral structures of this size. In the axial direction, structures in the millimeter range can be realized.
There is no general answer to this question as the time is highly dependent on the object to be printed. There is a clear trade-off between resolution and speed. For our current MergeOne solution print speeds in the range up to 1 mm3/h can be reached. Other future print heads will enable up to 10 mm3/h. The pure printing speed is neither determined by our technology nor our system. Manufacturers of 2PP systems have made considerable progress here in recent years. Current 2PP systems are already 10x faster than systems one to two years ago. Those systems are, thus, not only ideally suited for prototyping, but are already competitive for small series. Against the backdrop of current innovations among manufacturers, the profitability threshold in terms of unit numbers is being pushed ever higher in favor of 3D microprinting.
After printing, the printed object is removed from the printer. Usually, the non-polymerized material is removed with a developer. In this process, all materials are developed together. Typical developers are PGMEA, IPA and mr-DEV600. No post-UV-curing is necessary, but is recommended for certain writing strategies.
It can be printed on almost any surface that can be brought into the printer. These can be wafers, but also active devices such as VCSELs.
How does the print object adhere to the substrate, i.e. how does it adhere to the surface to be printed?
The most commercial materials do have a high adhesion to commonly cleaned glasses, silicon and metals. Various typical adhesion promoters are available to increase adhesion. Appropriate procedures are specified by the manufacturers, and customers can also draw on HETEROMERGE’s years of experience at this point. Please contact us for advice.
Theoretically, voxel-by-voxel could be printed and different materials can be used for each voxel, but this would be very costly in time. Our system is most suitable for printing multiple layers of different materials. Variation within the layers is also possible enabling efficient multi-material printing.
Questions about printing optical structures
For optical structures, the printing parameters are usually selected so that individual lines are no longer visible. In this regard, resolution is not the prior metric. The surface roughness as more relevant metric can be below 10 nm RMS and thus a high optical quality in the range of lambda/100 in the visible wavelength spectrum is possible.
From publications, the damage threshold limit of the material at about 1 µm wavelength and ns/fs pulsed lasers is in the range of 1-10 J/cm2 as a first approximation.
What happens at the interface between the printed material layers? Are optical effects to be expected here?
The interface represents a transition area of numerous properties. The advantage of the in situ material exchange is that it works without developing as an intermediate step. This means that it can be assumed that a maximum number of reactive groups can be achieved at the interface and is thus available for high adhesion of the materials. In addition, mixed phases may be present in a spatially very limited area, which can also contribute to improved adhesion. In principle, high adhesion can only be achieved if compatible materials are used in terms of polymerization mechanism as well as chemical composition. For most commercial materials as well as the materials of HETEROMERGE this is given. For non-compatible materials as well as materials with significantly differing material shrinkage, despite optimized exposure parameters, improved adhesion can be achieved by a matching layer or certain mechanic support structures for optics.
With the current objective adapters, write fields of up to 400 µm can be made possible. In addition, larger optics can be fabricated up to the millimeter range by stitching. Refractive and diffractive optics as well as meta-optics can be printed. Through the MergeOne system, materials of different optical properties can be combined, thus providing a solution to the challenge of improved optical systems such as the correction of aberrations and the integration of different properties such as focusing and filtering with fewer optical elements.
Yes, that is possible. Other diffractive optics can also be printed.
The printing materials do have acceptable to very good values for optical losses, depending on the wavelength range used. For example, boundary surfaces create additional interfaces and reflections like in any composite optics. The largest reflections occur at the interface to air. Here, established antireflection and matching coatings can be considered.
There are materials such as Ormocere® which are already established in industrial use, especially at high temperatures (e.g. reflow processes), and which deliver very good properties. Those materials can be also used for the typical range of temperature of electronic devices.
Printing can take place at module level or at wafer level. In this case, the laser diode or at lest the coupling facet/active material might come into direct contact with the printing material. In principle, however, printing can also be done on corresponding module carriers, which are then aligned with the laser diode for sensitive active regions. In the latter case, however, the packaging density is significantly lower.
Yes, this is possible. Almost any free form can be printed. Also the substrate is quite variable for our MergeOne system.
Yes, as long as the laser can still achieve the necessary laser power at the focal point. For many materials, good transparency is given in the wavelength range of 780 nm used.
Yes, this is not a problem.
Verification is performed by standard metrology methods such as confocal microscopy or mechanical stylus methods.
We have printed current examples for optical and biological applications. For the proof of functionality, we are currently working intensively with corresponding customers and partners. If these results are available to the public, we will publish them accordingly.