Archive for the ‘Uncategorized’ Category

Harvest Imaging Forum 2015 : 3D Imaging with ToF

Wednesday, July 29th, 2015

The first session (10/11 Dec.) of the 2015 Harvest Imaging Forum is SOLD OUT.  Apparently Time-of-Flight is still a hot topic in the field.

There are still seats available for the second session (14/15 Dec.).

Albert, 29-07-2015.

Harvest Imaging Forum : 3D Imaging with ToF

Thursday, July 2nd, 2015

I just want to give an update on the status of registrations :

- for the first session (10/11 Dec. 2015) 2 seats are left,

- for the second session (14/15 Dec. 2015) several seats are still available.

Some people were asking why such a hurry for a forum that will take place in 6 months from now ?  The reason has to do with the hotel reservation : to get an acceptable rate for the meeting package and for the rooms, the cancellation options offered by the hotel are very limited.  So to make sure that I can give a final GO/NO GO to the hotel without extra financial penalties, early as well as firm participant registrations are needed.  Thanks for your understanding.

Albert, 02-07-2015.

International Image Sensor Workshop 2015 : Conversion Gain Engineering

Thursday, July 2nd, 2015

Several IISW2015 papers dealt with the attempt to obtain a large conversion gain to bring down the noise floor (expressed in noise equivalent electrons) of the imagers.  With a noise floor down to 0.25 electrons, a “standard” CIS could be applied in single electron detection. [Deliberately I do not call it "single photon detection" because we never have a QE of 100 %, so by definition we do not detect every photon.  The intention of the conversion gain engineering is to detect a single electron present in the PPD and/or at the FD node.]

Tohoku University demonstrated how to extract the various components of the floating diffusion capacitance, and to further lower this capacitance.  Their mainn focus was lowering the concentration of the FD junction and working without LDD at the drain side of the source follower.  A conversion gain of 243 uV/electron is reported.  [LDD's are normally introduced to reduce the effect of hot carriers, what about the hot carriers in this structure without LDD ?]  In a second paper of the same group, the LDD-less FD structure was implemented in a real device.  To overcome the limitation of the small full well capacity with a large conversion gain, the pixel has applied the LOFIC technique in the pixel.

Dartmouth School of Engineering published their work on Multi-Bit Quanta Image Sensors by showing a measurement histogram indicating that single electron detection was realized.  The sensor used in the experiment had a conversion gain of 242 uV/electron (just 1 uV/electron lower than Tohoku Univ. !).  The paper is suggesting that a conversion gain of 1 mV/electron may be realized in the near future.  Is was not mentioned how this can be done.  But for sure very advanced CIS technologies of 65 nm or less are needed.

Also worthwhile to mention is the work of CEA, in which they use a p-type in-pixel readout structure to obtain a conversion factor of 185 uV/electron.  This is still not large enough to perform single electron detection, but is moving in the right direction.

Caeleste presented a small test array based on the pixel that was presented by the same group at ISSCC a couple of years ago.  The p-type source follower is swept between accumulation and inversion to make the 1/f noise uncorrelated between various multiple sampling moments.  Apparently there are still problems to solve in this structure, but besides that, a conversion factor around 400 uV/electron was reported for s 180 nm CIS technology.

A bit in the same direction as the papers described above, is the work reported by ON Semiconductor (former Truesense Imaging, former Kodak) describing an EM-CCD.  The overall concept is not new, but after TI and E2V, ON Semi is the next one to put EM-CCDs on the market.  With the EM concept, the primary goal is not to reach a large conversion gain, but to reach very low (equivalent) noise levels.  To continue along the EM-line, E2V published their work on EM-CMOS, fabricated in a 0.18um process.

Albert, 02-07-2015.

 

International Image Sensor Workshop 2015 : Stacked Imagers

Tuesday, June 23rd, 2015

The fight on stacking has began.  After Sony’s presentation at ISSCC, others are following on the stacked road.  Omnivision shows their architecture on stacking with the TSV’s outside the imaging array.  They claim to have the technology ready to start production of stacked imagers with a pixel pitch of 1 um.  Olympus showed their improved work over the one presented two years ago at ISSCC.  Olympus has a contact between the two silicon layers for every group of 2×2 pixels.  They created a 16M pixel device with 4M direct contacts, each with 7.6 um pitch.  Extra added to the ISSCC paper is the CDS capability buried in the second layer of silicon.  Also remarkable : all circuitry on the top level silicon is p-type !  Because a metal light shield is used between the two layers of silicon, a PLS of -180 dB is obtained.  Giant steps forward in their stacked wafer-to-wafer imager process.

Like Olympys, also  NHK showed a wafer-to-wafer bonding using Au contacts.  Nice to get also some information about the technology of the bonding itself.  TSMC had a paper about the photon emission in a stacked CIS.  Of course the second layer with the processing circuitry in a stacked image sensor is not designed/optimized for imaging purposes, and consequently during operation the circuitry present in this layer can generate some light that can be captured by the top layer.  This is no longer PLS but SLP, because the light is coming in the opposite direction.  Also the last paper in this session came from TSMC and dealt with dark FPN improvement by a stacked CIS process.  Focus was put on the decomposition of the FPN by biasing/switching the TG in an appropriate way.

Albert, 23-06-2015.

International Image Sensor Workshop 2015 : Image Sensors for Digital Photography

Monday, June 22nd, 2015

The first session of IISW2015 was devoted to larger devices intended for digital still photogrpahy.  Samsung presented a 28M APS-C sensor with BSI technology.  It is not common to go after BSI for these large dies, but apparently time and yield is ready to apply BSI to these larger devices as well.  Remarkable dark performance : 9 electrons/s dark current at 60 deg.C, 1.8 electron of random noise at 24 dB gain.  The architecture is charactereized by 1 ADC for 2 columns, double column busses and an optimized read sequence to allow for binning.

Canon described their sensor with phase-detection auto-focus pixels in EVERY pixel.  This solution allows for no light shield in the auto-focus pixels and no interpolation of the auto-focus pixels.  This sensor is already avaialable in Canon cameras, but it is the first time Canon publishes technical information about the device.  Because of the dual photodiode in every pixel, every pixel is provided with two readout structures, so every pixel has 8 transistors.  Random noise level of 1.8 electrons is reported at gain = 32 for a single photodiode.

Also Sony presented a CMOS imager with auto-focus functionality in every pixel.  This sensor is provided with a diagonal pixel orientation, so that the rows have alternatively G pixels and R/B pixels.  To make this sensor compatible with the installed software base, first of all the pixel stream is converted into Bayer RGB.  Also of interest for this sensor architecture with a dual PD in every pixel is the option for HDR by using 1 PD/pixel for a short exposure and 1 PD/pixel for a long exposure time.

Teledyne DALSA published one of the very few CCD papers at the workshop, mainly large area devices, e.g. 32M, 60M and 250M.  Remarkable is the ultra low dark current for these devices : 2 pA/cm2 at 60 deg.C.  These low values make these devices very well suited for extremely large expsoure times.

 

Albert, 22 juni 2015.

International Image Sensor Workshop 2015 : General Trends

Friday, June 19th, 2015

Some interesting trends in image sensor technology for consumer applications are :

- the incorporation of deep trench isolation (DTI) between the pixels to lower the optical and electrical cross talk.  Announced were already DTI defined from the front side (ST) as well as the back side (Samsung), but new at the workshop are the DTIs that do not completely go through the thinned BSI silicon,

- building “walls” between the colour filters (called “buried CFA”) is finding its way to production.  These walls limit optical and spectral cross-talk,

- very thin optical stacks, down to 1.5 um for BSI sensors,

- incoroporation of focus pixels for auto-focusing purposes.  These focus pixels can be incorporated in a regular pattern, but sometimes a semi-random pattern is used as well.  Moreover, the focus pixels do not need to be all of the same size,

- stacked imager are more and more introduced.  During IISW 2009, the buss word was BSI, now it is “stacked”.  Stacked imagers are going to solve all the problems ….

- the incorporation of W pixels continues, in more recent devices, up to 50 % of the pixels are W pixels.

In conclusion : no major new technologies were introduced, neither any pixel size below 1 um, but everything is getting better in performance and more compact in size.

Albert, 19/06/2015.

Third HARVEST IMAGING FORUM

Saturday, June 13th, 2015

As already announced earlier, also in 2015 there will be a Harvest Imaging Forum.  All forum information is now on-line, including agenda and registration form.  More info can be found at  www.harvestimaging.com/forum.php

Albert, 13-06-2015.

 

Third HARVEST IMAGING FORUM in December 2015

Tuesday, May 5th, 2015

After a very successful forums in 2013 and 2014, a third one will be organized in December, 2015, in Voorburg (the Hague), the Netherlands.  The basic intention of the forum is to have a scientific and technical in-depth discussion on one particular imaging topic.  The audience will be strictly limited to enhance and stimulate the interaction with the speaker(s) as well as to allow close contacts between the participants.

The subject of the third forum will be :

“3D Imaging with Time-of-Flight :

Solid-State Devices, Circuits and Architectures”.

 A world-level expert in the field,

dr. David STOPPA,

is invited and agreed to address and explain the ins and out of this important topic.

The agenda of the forum will be published soon, registration for the forum will start after the IISW2015.

 

Albert, 5/5/2015.

Announcement of the third HARVEST IMAGING FORUM in December 2015

Friday, April 17th, 2015

Mark now already your agenda for the third harvest imaging forum (or solid-state imaging forum as we called it earlier), scheduled for Dec. 10-11, 2015.

After the succesful gatherings in 2013 and 2014, I am happy to announce a third one.  Also this third Harvest Imaging forum will be a high-level, technical, short course focusing on one particular hot topic in the field of solid-state imaging.  The audience will be strictly limited, just to stimulate as much as possible the interaction between the participants and speaker(s).  The subject of the third forum will be : “3D Time-of-Flight Imaging”.

More information about the speaker and the agenda of the third forum will follow in the coming weeks, but I wanted to share this announcement with you as early as possible to make sure you can keep your agenda free on these days.

Albert,

April 17th, 2015.

Imaging Trainings scheduled for Spring 2015

Wednesday, April 8th, 2015

Maybe it is good to remind the visitors of this blog about imaging trainings in the Spring 2015.  There are still 3 different courses in the pipeline :

- a 2-day class to get an introduction in the world of CMOS image sensors.  This class is intended for people who have almost no background in solid-state imaging.  This course takes place in Delft on May 6-7, 2015.  Organization through www.fsrm.ch.

- a 5-day class if you want to learn more about imagers than just the working principles.  Also this class is intended for “new-comers” in the field, but also people working already a few years in imaging can revitalize their knowledge.  Key to this class are the exercise sessions at the end of every day helping the participants to put the theory into practice.   This course takes place on May 18-22, 2015 in Barcelona, and is organized by www.cei.se.

- a 2-day class with hands-on measurements and evaluation of an “unknown” camera.  Because the participants have to perform all characterization work themselves, this course is NOT intended for people fresh in the imaging field.  Preferably the course participants have a few years of experience in the arena of solid-state imaging.  This course takes place in Munich, on June 2-3, 2015, organized by www.framos.com.

Albert, 8 april 2015.