It’s not all done with mirrors

7 September 2021, Fremont

G&H acousto-optic deflectors allow for repeatable precision, at ultra-high speed

G&H’s acousto-optic deflectors hit the mark for industry and research alike

Steering a laser beam accurately and rapidly onto target to perform intricate micro-materials processing tasks is critical to success in many applications.

Arron Campi, Acousto-Optic Product Manager
Arron Campi, Acousto-Optic Product Manager

This is particularly true in the consumer electronics, semiconductor and automotive industries where the demand for increased functionality, reduced size and low cost has driven manufacturers down a seemingly never-ending path of miniaturization. In-turn the manufacturing processes and equipment used in today’s fabs has had to evolve in response. Right at the heart of this evolution is G&H, with our range of acousto-optic deflectors (AODFs).

To explain why these components are becoming ever more indispensable in microelectronics material and semiconductor processing applications, it is worth briefly exploring the changing nature of those applications themselves – and of the lasers they ultimately rely on.

Acousto-optic beam deflector schematic
Acousto-optic beam deflector schematic

Every micron and every second counts

Laser scanning has been used for decades as a method to steer a laser beam across a target in either one or two dimensions. This enables rapid non-contact processes in hundreds of applications ranging from the rather mundane, such as supermarket scanners, laser light shows or laser markers to the amazing, such as high-speed PCB via drilling, lidar, UV wafer inspection, micrometer scale machining, wafer dicing, graphic imaging, and much more.

Why use a scanning laser? Because in all these applications the laser can process faster and with more accuracy and repeatability than any other technology. This maximizes throughput and yield, minimizing costs of manufacture, even as processes become more complex.

Take the example of dicing a semiconductor wafer, for example. In comparison to a traditional diamond saw, a laser can not only cut thinner kerfs, it can cut without damage to the fragile low-k materials in the wafer, maximising yield – and there is no need to replace any costly blades!

UV pulsed lasers, for their part, are growing in use and effectiveness in applications where efficient cutting and drilling of intricate features in materials with very little heat affect is a requirement.

Printed circuit board manufacturing machine

Naturally, however, lasers of whatever wavelength, rep rate or power are effectively useless if the technology to steer the beam onto target – or deflect it through the angles necessary to achieve this – is not up to the task. Traditionally the scanning technology most widely used has been mirrors mounted on galvanometer motors, these can be used alone or in a pair to create a 2D scan field. Naturally with a mechanical deflector there is a limit to the speed, accuracy and repeatability with which even a low inertia mirror can be moved by the motor, and in some applications we have effectively reached the limits for galvo scanners.

In fact, as we commented in our research in the recent G&H Insight paper, what distinguishes higher-throughput and more precise lasers for industrial use is ultimately “faster and more efficient photonic modules,” including, critically, “faster optical switches and deflectors.”

Our AODFs enable a “new age of solid-state optical scanning” – so let’s find out more.

Acousto-optic beam deflector
G&H UV acousto-optic beam deflector

Galvanometers and AODFs – what’s the angle?

For many industrial laser applications, scan field size is critical – and galvanometers (galvos) can certainly scan over a large angle, which accommodates a much larger scan field, more material and larger surfaces. However, the precision of the scanning within the scan field is limited.

AODFs, by contrast, have a limited scan angle, but offer far more precision than galvos can. For this reason, they are generally used together with a galvo to increase the precision of the beam location.  AODFs can move the beam far more quickly, so it can image many high precision features within a small scan field as the galvo either slowly sweeps across its scan field, or moves rapidly from location to location in a step and repeat method.  

The combination of galvos for macro positioning and AODF’s for fine beam positioning can facilitate higher-throughput manufacturing processes, with tighter control.

High scan speeds, excellent positional accuracy and repeatability are core benefits of AODF technology, and this is particularly relevant for processes like via drilling in rigid and flex PCBs, as the number and density of the holes to be drilled has increased.

It’s also worth noting, that in a galvo-only based system, the laser needs to be shuttered or gated off when it is not needed for processing (for example, when it needs to traverse from one position to another) and in addition it is difficult to vary the intensity of the laser in real time. AOTFs, however, fulfil both these roles.

In short, a more exacting task must now be performed more quickly and reliably, at a level of speed and precision that typically exceeds that of traditional scanning systems – and here, again, AODFs deliver.

So, how do they achieve this?

Performance and reliability: the heart of an AODF

The answer to this question lies not only in what is in the AODF device itself, but what comes before and after it.

We have already hinted above that combining AODF devices with galvanometers tends to produce a superior scanning result, and this is because combining a mechanical deflector with an optical deflector optimizes the relationship between deflection velocities versus deflection angles.

However, the input to the deflector comes from an RF driver that generates a signal to create an acoustic wave within the crystal of the AODF (or indeed other acousto-optic device), whose frequency and intensity then determine how the optical beam is modulated, deflected, or tuned.

It is naturally important that the right driver should be selected to optimize speed, stability, and functional efficiency for each specific application, and as our AO product lines expand, we are creating more flexible, adaptive RF drivers to accommodate powerful functionality and high levels of performance across many and varied applications without the need for new hardware, whilst still offering custom OEM designs optimized to each customer’s requirement.

When it comes to what’s inside the AODF device, as with all our acousto-optic devices, we incorporate high-quality crystals and anti-reflection (AR) coatings, for maximum efficiency and output, and minimal loss.

In addition to tellurium dioxide crystals that we grow ourselves, we also offer sapphire and crystalline quartz to enable the higher power output vital for many industrial applications.

Resilience, too, is important. The AODF range is housed in a rugged package, in a solid-state design that offers unsurpassed reliability, consistency, and temperature stability, even in volume manufacturing.

These characteristics have helped cement AODF’s status as a required technology in many industrial applications, but it is also playing a pivotal role in research applications too, some of which we explore below.

RF driver, acousto-optic beam deflector
G&H RF 600 series driver

Meeting new challenges with innovative solutions

G&H’s commitment is to change the world with photonics, and we invest heavily in research and development, as well as in strategic relationships with academic and industry partners (including the European Photonics Industry Consortium – EPIC) to this end.

Currently, we are working with a number of academic institutions to further develop acousto-optic components in several key directions, including “deep UV” wavelength applications (between 280 nm and 200 nm), and optical memory devices.

Additionally, at the University of Birmingham in the UK, our acousto-optic components are being used for quantum research – a discipline that depends on the ability to manipulate and control tiny objects, such as photons, at extraordinary levels of exactitude.

For industry and research alike, then, G&H’s expertise in acousto-optic devices is meeting new challenges with innovative solutions for now and the future – and that hits the mark for us and for our customers alike.