amsOSRAM announces new sensor Mira220

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  • New Mira220 image sensor’s high quantum efficiency enables operation with low-power emitter and in dim lighting conditions
  • Stacked chip design uses ams OSRAM back side illumination technology to shrink package footprint to just 5.3mm x 5.3mm, giving greater design flexibility to manufacturers of smart glasses and other space-constrained products
  • Low-power operation and ultra-small size make the Mira220 ideal for active stereo vision or structured lighting 3D systems in drones, robots and smart door locks, as well as mobile and wearable devices

Press Release:

Premstaetten, Austria (14th July 2022) -- ams OSRAM (SIX: AMS), a global leader in optical solutions, has launched a 2.2Mpixel global shutter visible and near infrared (NIR) image sensor which offers the low-power characteristics and small size required in the latest 2D and 3D sensing systems for virtual reality (VR) headsets, smart glasses, drones and other consumer and industrial applications.

The new Mira220 is the latest product in the Mira family of pipelined high-sensitivity global shutter image sensors. ams OSRAM uses back side illumination (BSI) technology in the Mira220 to implement a stacked chip design, with the sensor layer on top of the digital/readout layer. This allows it to produce the Mira220 in a chip-scale package with a footprint of just 5.3mm x 5.3mm, giving manufacturers greater freedom to optimize the design of space-constrained products such as smart glasses and VR headsets.

The sensor combines excellent optical performance with very low-power operation. The Mira220 offers a high signal-to-noise-ratio as well as high quantum efficiency of up to 38% as per internal tests at the 940nm NIR wavelength used in many 2D or 3D sensing systems. 3D sensing technologies such as structured light or active stereo vision, which require an NIR image sensor, enable functions such as eye and hand tracking, object detection and depth mapping. The Mira220 will support 2D or 3D sensing implementations in augmented reality and virtual reality products, in industrial applications such as drones, robots and automated vehicles, as well as in consumer devices such as smart door locks.

The Mira220’s high quantum efficiency allows device manufacturers to reduce the output power of the NIR illuminators used alongside the image sensor in 2D and 3D sensing systems, reducing total power consumption. The Mira220 features very low power consumption at only 4mW in sleep mode, 40mW in idle mode and at full resolution and 90fps the sensor has a power consumption of 350mW. By providing for low system power consumption, the Mira220 enables wearable and portable device manufacturers to save space by specifying a smaller battery, or to extend run-time between charges.

“Growing demand in emerging markets for VR and augmented reality equipment depends on manufacturers’ ability to make products such as smart glasses smaller, lighter, less obtrusive and more comfortable to wear. This is where the Mira220 brings new value to the market, providing not only a reduction in the size of the sensor itself, but also giving manufacturers the option to shrink the battery, thanks to the sensor’s very low power consumption and high sensitivity at 940nm,” said Brian Lenkowski, strategic marketing director for CMOS image sensors at ams OSRAM.

Superior pixel technology

The Mira220’s advanced back-side illumination (BSI) technology gives the sensor very high sensitivity and quantum efficiency with a pixel size of 2.79μm. Effective resolution is 1600px x 1400px and maximum bit depth is 12 bits. The sensor is supplied in a 1/2.7” optical format.

The sensor supports on-chip operations including external triggering, windowing, and horizontal or vertical mirroring. The MIPI CSI-2 interface allows for easy interfacing with a processor or FPGA. On-chip registers can be accessed via an I2C interface for easy configuration of the sensor.

Digital correlated double sampling (CDS) and row noise correction result in excellent noise performance.

ams OSRAM will continue to innovate and extend the Mira family of solutions, offering customers a choice of resolution and size options to fit various application requirements.

The Mira220 NIR image sensor is available for sampling. More information about Mira220.

Mira220 image sensor achieves high quantum efficiency at 940nm to allow for lower power illumination in 2D and 3D sensing systems
Image: ams

The miniature Mira220 gives extra design flexibility in space-constrained applications such as smart glasses and VR headsets
Image: OSRAM

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Preprint on unconventional cameras for automotive applications

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From --- You Li et al. write:

Autonomous vehicles rely on perception systems to understand their surroundings for further navigation missions. Cameras are essential for perception systems due to the advantages of object detection and recognition provided by modern computer vision algorithms, comparing to other sensors, such as LiDARs and radars. However, limited by its inherent imaging principle, a standard RGB camera may perform poorly in a variety of adverse scenarios, including but not limited to: low illumination, high contrast, bad weather such as fog/rain/snow, etc. Meanwhile, estimating the 3D information from the 2D image detection is generally more difficult when compared to LiDARs or radars. Several new sensing technologies have emerged in recent years to address the limitations of conventional RGB cameras. In this paper, we review the principles of four novel image sensors: infrared cameras, range-gated cameras, polarization cameras, and event cameras. Their comparative advantages, existing or potential applications, and corresponding data processing algorithms are all presented in a systematic manner. We expect that this study will assist practitioners in the autonomous driving society with new perspectives and insights.

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Black Phosphorus-based Intelligent Image Sensor

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Seokhyeong Lee, Ruoming Peng, Changming Wu & Mo Li from U-Dub have published an article in Nature Communications titled "Programmable black phosphorus image sensor for broadband optoelectronic edge computing".

Our blog had advertised a pre-print version of this work back in November 2021:

Abstract: Image sensors with internal computing capability enable in-sensor computing that can significantly reduce the communication latency and power consumption for machine vision in distributed systems and robotics. Two-dimensional semiconductors have many advantages in realizing such intelligent vision sensors because of their tunable electrical and optical properties and amenability for heterogeneous integration. Here, we report a multifunctional infrared image sensor based on an array of black phosphorous programmable phototransistors (bP-PPT). By controlling the stored charges in the gate dielectric layers electrically and optically, the bP-PPT’s electrical conductance and photoresponsivity can be locally or remotely programmed with 5-bit precision to implement an in-sensor convolutional neural network (CNN). The sensor array can receive optical images transmitted over a broad spectral range in the infrared and perform inference computation to process and recognize the images with 92% accuracy. The demonstrated bP image sensor array can be scaled up to build a more complex vision-sensory neural network, which will find many promising applications for distributed and remote multispectral sensing.

It is now peer reviewed and officially published as an open access paper:

Peer review report and authors' responses are also publicly available. In particular, it is interesting to see the response to some comments and about pixel non-uniformities, material stability during etching and longevity of the sensor prototype. 

Some lightly edited excerpts from the reviews and authors responses below:

Reviewer: The optical image of the exfoliated flake clearly shows regions of varying thickness. How did the authors ensure each pixel is of the same thickness? 

Authors: The mechanically exfoliated bP has several regions with different thicknesses. We fabricated all the pixels within a large region with uniform optical contrast, as outlined by the red dotted line, indicating uniform thickness. The thickness of the region is also confirmed with atomic force microscopy.

Reviewer: There is hardly any characterisation data provided for the material. How much of it is oxidised?

Authors: The oxidation of bP, it is indeed a concern. To mitigate that, we exfoliated and transferred bP in an Ar-filled glovebox. The device was immediately loaded into the atomic layer deposition (ALD) chamber to deposit the Al2O3 / HfO2 /Al2O3 (AHA) multilayers, which encapsulate the bP flake to prevent oxidation and degradation. This has been a practice reported in the literature, which generally leads to oxidation of only a few layers. Thanks to the 35 nm thick AHA encapsulation layer, our device shows long-term stability with persistent electrical and optical properties for more than 3 months after fabrication. We discuss that in the response to question 7. Furthermore, Raman spectroscopy shows no sign of Px Oy or Hx POy forming during the fabrication process. Thus, we expect that the oxidation of bP flake is no more than 3 layers (or 1.5 nm), which, if any, marginally affects the optical and electrical properties of the bP-PPT device. 

Reviewer: Why did the authors focus only on the IR range when the black phosphorus can be even more broadband into the visible at the thickness used here?

Authors: The photoresponsivity of black phosphorus certainly extends to the visible band. We have
utilized both the visible and the IR range by engineering the device with the AHA stack: IR light to input images for optoelectronic in-sensor computing; visible light to optically program the device by activating the trapped charges and process the encoded images such as pattern recognition.

Reviewer: How long do the devices keep working in a stable manner?

Authors: We agree with the reviewer that more lifetime measurement data is important to ensure the
stability of the device’s operation. We have evaluated the performance of the bP-PPT devices over a long period of time (up to 3 months) ... the gate modulation, memory window, on-off ratio, and retention time of our devices remain consistent even 3 months after they were fabricated.

In today's day and age of Twitter, it's refreshing to see how science really progresses behind the scenes --- reviewers raising genuine concerns about a new technique; authors graciously accepting limitations and suggesting improvements and alternative ways forward.

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