Martin Bring

One-Megapixel Monocrystalline-Silicon Micromirror Array on CMOS Driving Electronics Manufactured With Very Large-Scale Heterogeneous Integration

In this paper, we demonstrate the first high-resolution spatial-light-modulator chip with 1 million tilting micromirrors made of monocrystalline silicon on analog high-voltage complementary metal-oxide-semiconductor driving electronics. This device, as result of a feasibility study, shows good optical and excellent mechanical properties. The micromirrors exhibit excellent surface properties, with a surface roughness below 1-nm root mean square. Actuated micromirrors show no imprinting behavior and operate drift free. Very large-scale heterogeneous integration was used to fabricate the micromirror arrays. The detailed fabrication process is presented in this paper, together with a characterization of the SLM devices. Large arrays of individually controllable micromirrors are the enabling component in high-perfomance mask-writing systems and promising for high throughput deep-ultraviolet maskless lithography systems. The adoption of new materials with enhanced characteristics is critical in meeting the challenging demands with regard to surface quality and operation stability in the future. Very large-scale heterogeneous integration may enable virtually any solid-state material to be integrated together with CMOS electronics.

CMOS-Integrated Si/SiGe Quantum-Well Infrared Microbolometer Focal Plane Arrays Manufactured With Very Large-Scale Heterogeneous 3-D Integration

We demonstrate infrared focal plane arrays utilizing monocrystalline silicon/silicon-germanium (Si/SiGe) quantum-well microbolometers that are heterogeneously integrated on top of CMOS-based electronic read-out integrated circuit substrates. The microbolometers are designed to detect light in the long wavelength infrared (LWIR) range from 8 to 14 μm and are arranged in focal plane arrays consisting of 384 × 288 microbolometer pixels with a pixel pitch of 25 μm × 25 μm. Focal plane arrays with two different microbolometer designs have been implemented. The first is a conventional single-layer microbolometer design and the second is an umbrella design in which the microbolometer legs are placed underneath the microbolometer membrane to achieve an improved pixel fill-factor. The infrared focal plane arrays are vacuum packaged using a CMOS compatible wafer bonding and sealing process. The demonstrated heterogeneous 3-D integration and packaging processes are implemented at wafer-level and enable independent optimization of the CMOS-based integrated circuits and the microbolometer materials. All manufacturing is done using standard semiconductor and MEMS processes, thus offering a generic approach for integrating CMOS-electronics with complex miniaturized transducer elements.

Fabrication of large-scale mono-crystalline silicon micro-mirror arrays using adhesive wafer transfer bonding

Today, spatial light modulators (SLMs) based on individually addressable micro-mirrors play an important role for use in DUV lithography and adaptive optics. Especially the mirror planarity and stability are important issues for these applications. Mono-crystalline silicon as mirror material offers a great possibility to combine the perfect surface with the good mechanical properties of the crystalline material. Nevertheless, the challenge is the integration of mono-crystalline silicon in a CMOS process with low temperature budget (below 450°C) and restricted material options. Thus, standard processes like epitaxial growth or re-crystallization of poly-silicon cannot be used. We will present a CMOS-compatible approach, using adhesive wafer transfer bonding with Benzocyclobutene (BCB) of a 300nm thin silicon membrane, located on a SOI-donor wafer. After the bond process, the SOI-donor wafer is grinded and spin etched to remove the handle silicon and the buried oxide layer, which results in a transfer of the mono-crystalline silicon membrane to the CMOS wafer. This technology is fully compatible for integration in a CMOS process, in order to fabricate SLMs, consisting of one million individually addressable mono-crystalline silicon micro-mirrors. The mirrors, presented here, have a size of 16×16 μm2. Deflection is achieved by applying a voltage between the mirrors and the underlying electrodes of the CMOS electronics. In this paper, we will present the fabrication process as well as first investigations of the mirror properties.

Very large scale heterogeneous system integration for 1-megapixel mono-crystalline silicon micro-mirror array on CMOS driving electronics

In this paper we demonstrate the first high mirror-count 1-level spatial light modulator (SLM) chip with 1 million tilting micro-mirrors made of mono-crystalline silicon on analogue, high-voltage CMOS driving electronics. The device from a feasibility study shows good optical and excellent mechanical properties. The micro-mirrors exhibit excellent surface properties with a surface roughness below 1 nm RMS, actuated micro-mirrors show no imprinting behavior and operate drift-free. Very large scale heterogeneous system integration was used to fabricate the micro-mirror array; the process is presented in this paper together with a characterization of the fabricated device.

Technology development of diffractive micromirror arrays for the deep ultraviolet to the near infrared spectral range

A new generation of micromirror arrays (MMAs) with torsional actuators is being developed within the European research project MEMI in order to extend the usable spectral range of diffractive MMAs from deep ultraviolet into the visible and near infrared. The MMAs have 256 x 256 pixels reaching deflections above 350 nm at a frame rate of 1 kHz, which enables an operation in the target wavelength range between 240 nm and 800 nm. Customized driver electronics facilitates computer controlled operation and simple integration of the MMA into various optical setups. Tests in the visible wavelength range demonstrate the functionality and the high application potential of first MMA test samples.

Calibration of diffractive micromirror arrays for microscopy applications

We report on our investigation to precisely actuate diffractive micromirror arrays (MMA) with an accuracy of λ/100. The test samples consist of analog, torsional MEMS arrays with 65 536 (256x256) mirror elements. These light modulators were developed for structured illumination purposes to be applied as programmable mask for life science and semiconductor microscopy application. Main part of the work relies on the well known characterization of MEMS mirrors with profilometry to automatically measure and approximate the MMA actuation state with high resolution. Examples illustrate the potential of this strategy to control the tilt state of many thousand micromirrors within the accuracy range of the characterization tool. In a dynamic range between 0 and >250 nm the MMA deflection has been precisely adjusted for final MMA application in the deep-UV - VIS - NIR spectral range. The optical properties of calibrated MMAs are tested in a laser measurement setup. After MMA calibration an increased homogeneity and improved image contrast are demonstrated for various illumination patterns.

Multispectral characterization of diffractive micromirror arrays

The present article discusses an optical concept for the characterization of diffractive micromirror arrays (MMAs) within an extended wavelength range from the deep ultra-violet up to near-infrared. The task derives from the development of a novel class of MMAs that will support programmable diffractive properties between 240 nm and 800 nm. The article illustrates aspects of the achromatic system design that comprises the reflective beam homogenization with divergence control and coherence management for an appropriate MMA illumination as well as the transfer of phase modulating MMA patterns into intensity profiles for contrast imaging. Contrast measurements and grey scale imaging demonstrate the operation of the characterization system and reflect the encouraging start of technology development for multispectral, diffractive MMAs.

High performance LWIR microbolometer with Si/SiGe quantum well thermistor and wafer level packaging

An uncooled microbolometer with peak responsivity in the long wave infrared region of the electromagnetic radiation is developed at Sensonor Technologies. It is a 384 x 288 focal plane array with a pixel pitch of 25μm, based on monocrystalline Si/SiGe quantum wells as IR sensitive material. The high sensitivity (TCR) and low 1/f noise are the main performance characteristics of the product. The frame rate is maximum 60Hz and the output interface is digital (LVDS). The quantum well thermistor material is transferred to the read-out integrated circuit (ROIC) by direct wafer bonding. The ROIC wafer containing the released pixels is bonded in vacuum with a silicon cap wafer, providing hermetic encapsulation at low cost. The resulting wafer stack is mounted in a standard ceramic package. In this paper the architecture of the pixels and the ROIC, the wafer packaging and the electro-optical measurement results are presented.