Harvest Imaging Blog

Good Bye 2015 ! 

At the very end of 2015, it is good to take a look backwards to see what 2015 has brought.

Actually I can start with the same statement as last year : “It was a busy year for Harvest Imaging”.  Several imaging trainings were organized, in-house as well as public courses.  Thanks to CEI, FSRM and Framos who organized the public or open courses.  Thanks to all my customers for the in-house courses.   Thanks to all participants for being there, because without participants there will be no trainings !  And apparently the imaging business is doing very well, because a lot of companies have hired new imaging engineers and consequently they are again asking for more trainings in 2016.  That is of course the best feedback I can get : returning customers. 

The Harvest Imaging Forum 2015 was targeting “3D Imaging with ToF”.  I was very happy to get the possibility to attract David Stoppa as the speaker for this forum.  The two sessions in December got very good feedback from the participants, and in January 2016 a third (and last) session will be organized.  The only drawback : the expectations for the third session are high, so David knows what to do.  At this moment I can announce already that also n 2016 another Harvest Imaging forum will be organized.  Topic and speaker(s) are still to be defined.

In 2015 Harvest Imaging came with a new product on the market : a reverse engineering report of a particular imaging feature present in a commercial camera.  The first reverse engineering report was devoted to Phase Detection Auto-Focus Pixels.  This is a very interesting topic, very well described in patents of several Japanese camera manufacturers, but the technical results obtained by these PDAF pixels are hardly described in public literature.  For that reason Harvest Imaging started working on it.  At the end of the road, a nice report is ready and is for sale.  And one of the conclusions is that it took more time and effort than originally planned.  (This is in line with the 3^rd law of Hofstadter : A project always takes longer than originally scheduled, even if you take the 3^rd law of Hofstadter into account).  But it still was worthwhile doing it.  We learned a lot from the PDAF measurements.  And if a “good” subject pops up in 2016, a new reverse engineering effort will start.

If I look back to the activities that took place in relation to the imaging society (IISS), then Harvest Imaging took a very active role in the organization of the 2015 International Image Sensor Workshop.  In close cooperation with imaging peers (Johannes Solhusvik and Pierre Magnan) a successful workshop was organized.   About 100 technical papers were presented during almost 4 days.  But also remarkable : during the social activity of the workshop, all 180 participants went out for biking in an old cave.  Their reactions afterwards were quite interesting : most of them enjoyed it very much, a few much less.

As you can read, 2015 was very busy and was interesting because it was so diverse.  I do hope that the customers of Harvest Imaging can close 2015 with a big smile on their face.  I would to thank all of them for the business in 2015 and I am looking forward to serve them again in 2016.

Welcome 2016 !  Looking forward to another successful year, although without an IISW, but with a new special issue of IEEE Transactions on Electron Devices on Image Sensors coming up !

Wishing all my readers a Merry Christmas and a Happy New Year.  “See” you soon.

Albert, 23-12-2015.

Time-Delayed Integration or TDI in CMOS seems to be a hot topic (at least for space applications), but it also still is a challenging architecture to build in CMOS technology.  At the CNES CMOS image sensor workshop in Toulouse (held about 10 days ago), there were several presentations on CMOS-TDI, here is an overview.

C. Virmentois presented the CNES work on TDI.  They finished several projects with ESPROS (CCD on CMOS), IMEC (CCD on CMOS) and ST (digital CMOS TDI).  At this moment work is going on in the field of a multi-spectral TDI with large pixels, also this latest device is based on a digital TDI.

W.r.t. to the chip(s) made at ESPROS, the following details were given :

• Fully depleted, BSI,
• 7.5 um and 6.5 um pixel pitch for monochrome,
• 26 um and 52 um pixel pitch for multi-spectral,
• noise level of 600 uV,
• dark current of 2.6 nA/cm2 at 20 ^oC,
• conversion gain : 10… 15 uV/e^–,
• CTI : 2.10^-3,
• INL < 1.5 %,
• FWC : 92 ke^– at 1 V,
• QE > 70 % n-IR.

A second chip made at ESPROS showed improved results, such as :

• Noise : 350 uV,
• Dark current : 1ke^–/s (= 10 x less),
• CTI : … 1.10^-4 …

During the presentation it was not mentioned which part of the processing was done by ESPROS and/or which part of the processing was done by a third party.

M.-Y. Yeh of NAR Labs reported the work on TDI done in his lab :

• 6 lines, 2 PAN + 4 multi-spectrum,
• 7.5 um pixel pitch for PAN and 30 um pixel pitch for multi-spectrum,
• Based on 4T BSI 2.5 um pixels, made in TSMC 0.11 um process,
• Stitched with 8 blocks next to each other, chip width : 12.288 cm.

F. Mayer of e2v mentioned that the first TDI made by his company was already done in 2010 with charge transfer in a 0.18 um CMOS process.  Later more CCD-like devices were made.

For the digital domain, Frederic mentions :

• Too much load for the ADC,
• Motion MTF issues,
• Dynamic range is OK, but the noise is pretty high.

For the charge domain :

• Limitation in full-well capacity.

The combination of digital and charge domain can overcome a number of drawbacks, but the architecture will be pretty complex.

The first generation charge transfer TDI was built on a surface channel CCD, the second generation was provided with a buried channel.

Neither in this presentation the fab was mentioned that fabricated the CMOS wafers.

Ben-Ari of SemiConductors Devices gave a large list of performance data of the TDI’s made by his company.

In summary :

• 4 independent TDI arrays,
• digital running TDI with global shutter,
• 0.18 um technology,
• Chip size : 84 x 16 mm², 2600 pixels x 8 to 64 pixels,
• Full well : 300 ke^–, < 80 e^– noise, and 72 dB dynamic range,
• 50 … 10,000 lines/s,
• Dark current < 400 e^–/s at 25 ^oC,
• Single slope ADC,
• Stitched in 1 dimension,

Current status of these devices : BSI delivered, wafer sort done with good yield.

Boulenc gave an overview of IMEC’s TDI status :

• 0.13 um, CMOS flow with 3.3 V and 1.5 V power supply,
• Generation 1 (see also CNES presentation) with lateral AB and dedicated implants at the output to make it BSI compatible,
• Generation 2 : 5 um pixel size, 1025 x 512 pixels, gate spacing between 100 nm and 180 nm, CF : 25 uV/e^–, 2.5 nA/cm² dark current at 25 ^oC, 0.5 mV noise floor and 17 ke^– full well capacity,
• Generation 3 is in development.

In conclusion : a lot of interesting work is going on in the field of TDI-CMOS, but apparently none of the developments has yet resulted in commercially available devices with a performance that matches the existing TDI-CCD performance.  It is more difficult than expected to beat the TDI-CCD noise-free charge transfer in sub-pixel steps in combination with a low dark current.  Depending on which side of the table you are sitting, this can be bad news (for the customers eagerly waiting for TDI-CMOS) or this can be good news (for the engineers, because there are still enough challenging developments ahead of us).

Albert, 26-11-2015.