Example 7: custom sensors - Helicon Thin Film Systems, Ltd

THIN FILM SERVICES / APPLICATION AREA

custom thin film/thick film sensor coatings and packages

Example: Opto-electronic Test Sensors used in Flat-Panel Display Manufacturing

MATERIALS / APPLICATION AREA: Our sensor development contracts represent an exceedingly wide range of thin film applications - the applications in which our services are found useful typically involve discrete packaged sensors that rely on optical or electronic determination of pressure, temperature, strain (interferometric, transducive, etc), or gas components. Thin film applications within this area can comprise active or passive structures, hermetic sealing layers, diffusion bonded assemblies, electro-optic compounds, or unique combinations of known electronic/optical characteristics combined with unusual environmental or tribological requirements. Helicon has been involved in a large number of sensor development and upgrade projects, where such sensors almost invariably require the formation of thin film architectures on unusual substrates, which tend to incorporate a non-conventional geometry (cylinders, helices, optical fibers, ultra-thin membranes, etc.), unconventional materials, unconventional tolerances, or are subject to extreme conditions requiring atypical processing conditions.

EXAMPLE APPLICATIONS:

In the various sensor work taken on by Helicon Thin Film, one earlier application comprise high-permittivity sensors utilized for what are effectively capacitive sensors. Manufacturing of flat-panel displays requires critical testing of all circuits at the back-plane level. This is generally performed using what amounts to flying-head capacitance sensors that allow verification of localized electric fields.

Inset: image of Photon Dynamics' core module for flat-panel display testing, with Helicon-fabricated sensor membrane. In the image to left is one of Photon Dynamics Inc. flying-head optical sensors. Many of these sensor heads, utilizing Helicon's thin film product, are operating in the field as a result of the successful scale-up this process by Helicon Thin Film Systems at Helicon's facility, with the process eventually transferred to Photon Dynamics.

Helicon Thin Film Systems provided the facility and expertise for scale-up in manufacturing of the thin film component of sensors utilized for high-speed, go/no-go critical testing of the active pixel arrays in most present-day flat panel displays. This scaling of manufacturing was performed in conjunction with Photon Dynamics, Inc and Tucson Optical Research Corporation, where Gregory Lowe was spear-heading development of the thin film technology.

Further Applications With Low-temperature substrates/ Low thermal budgets: One challenge encountered in several types of sensors and detectors is the deposition of dense, reliable thin film stacks including high-temperatures compounds onto substrates that are very limited in their thermal stability, dimensionally and/or chemically. While energetic vapor deposition methods such as sputtering are inherently capable of non-equilibrium

DENSE, REFRACTORY METAL-OXIDE, DICHROIC MULTILAYERS ON DELICATE, ULTRA-THIN POLYMER SUBSTRATES

FORMING HIGH-TEMPERATURE MATERIALS ON LOW-TEMPERATURE SUBSTRATES

MECHANICAL STABILITY: ULTRA-THIN PELLICLE; 12-YEAR-OLD MULTI-LAYERS

MANUFACTURED AT HELICON

absolutely no buckling, crazing, shift, or loss of tension

materials formation, Helicon has developed several examples of what are arguably some of the most non-equilibrium process methods and apparatus known in thin film process technology, without concomitant damage from the ion bombardment normally associated with more energetic sputtering processes. One of the application areas wherein we apply this technical know-how is in the fabrication of material combinations that are entirely non-compatible by more equilibrium materials processing methods (e.g., not remotely possible by non-assisted evaporation, nor Atomic Layer Deposition, nor wet chemistry)

Figure: spectrophotometric aging data; no drift in spectral reflectance as a result of 10-year service.

Polymer Substrates:There are a growing number of applications that benefit from the formation of dense refractory compounds ( ) on relatively low-temperature substrates such as certain delicate polymeric materials. or very thin (<5 um) substrates of flexible films, such as at the bottom of the hicness range of biaxial PET (Mylar etc). For example, the figure on the right displays a <5um PET film, stretched over a square pellicle frame. Refractory oxides are deposited onto the PET (mylar) film in many quarter wave pairs to enable the desired dichroic properties.

The spectroscopic properties of such films are also witnessed to provid zero peak drift over this same period. Figure: high-permittivity sensor structures required formation of environmentally stable all-dielectric dichroic filters comprising dense refractory oxides on low-temperature polymers only several microns thick. initial post-deposition spectral reflectance vs after 10 years service life.

In sharp contrast to providing such multi-layers on a typical optical glass, providing these optical structures in the form of dense high-temperature compounds onto a low-temperature plastic film having exceedingly little thermal mass, and having this resulting materials system maintain stability in a state of uniform tension over a period of many years, is a distinctly different technical undertaking.

With regard to polymeric substrates, while those polymeric materials typically utilized for standard opthalmic purposes (e.g, polycarbonate) are fairly straightforward, less dimensionally/chemically stable polymer substrates can present unique requirements, if reliable coatings are to be realized. For example, some of our previous thin film work in injection-molded PMMA materials (for example, our work in disposable assay devices with surface plasmon resonance (SPR) based sensors) can represent specific challenges, depending upon such issues as the specific forming processes, plasticizers utilized, and the working fluids/vapors to which the product surface is exposed.

In addition to the ongoing development of moisture barriers films, other applications require substrates that have equally or greater requirements with regard to highly sensitive substrates that must nonetheless be conjoined with dense refractory materials. Please contact us if your organization is interested in pursuing these type of technical challenges - Helicon actively provides R&D, fabrication, and consulting in this area.