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Sunday, February 8, 2015

#319 Atomic-scale technology

Assigning physical dimension to an atom is a tricky proposition. Still, adopting some simplifications, radius of the atoms of elements in the periodic table of elements can be defined both empirically as well through calculations.


Recognizing adopted short cuts, we can assume for the purpose of this discussion that the size of the silicon atom is about 250 picometers or using more familiar unit of length about 0.25 nanometer.


Consider now that the semiconductor films thinner than 10 nm are readily available by means of Molecular Beam Epitaxy (MBE) and the thickness of MOSFET’s channel in ultra-thin body SOI can be controlled down to single nanometers which means that it can be made in the controlled fashion less than 20 atoms thick. Add to it one atom thick graphene which we have learned to form and manipulate pretty effectively and the term "atomic-scale technology" rather than "nanotechnology" seems to more adequately reflect state-of-the-art in semiconductor technology these days.


Posted by Jerzy Ruzyllo at 03:52 PM | Semiconductors | Link

Sunday, January 25, 2015

#318 14th Semiconductor cleaning symposium

This is to let you know that the 14th International Symposium on Semiconductor Cleaning Science and Technology (SCST 14) will be as usual organized under the auspices of ECS this time in Phoenix, AZ, Oct. 11-16, 2015. See the Call for Papers , consider submitting an abstratct by May 1, 2015 and coming to Phoenix to enjoy a very fine conference.

Posted by Jerzy Ruzyllo at 03:16 PM | Semiconductors | Link

Sunday, January 11, 2015

#317 "3.9" is an another number to remember.

Following on the "number to remember" theme, 3.9 is another number which is flat out remembered by those involved in semiconductor engineering.


The dielectric constant k of SiO2 is 3.9. What is special about this value is that it serves as a reference in defining what is a high-k dielectric and what is a low-k dielectric. In the broadly commonly accepted terminology the dielectrics featuring k>3.9 are referred to as high-k dielectrics and those featuring k < 3.9 as low-k dielectrics.
The high-k dielectrics are needed wherever strong capacitive coupling between two conductors separated by  the dielectric is needed. The most obvious example is a MOS gate stack where, since 45 nm technology generation, gate dielectrics featuring high-k are used so that adequate gate capacitance is maintined at the physically thicker dielectric.
The  demand for the low-k dielectrics is coming from the multi-level interconnect technology where the capacitive coupling between two interconnect lines is highly undesirable, and hence,  interlayer dielectrics featuring as low as possible dielectric constant must be used.


In the light of the key role both high-k and low-k dielectrics are playing, a "3.9" has become a number of great relevance in the advanced semiconductor engineering.  I found it interesting that some 15-20 years ago the issue of high- and low-k was not of much relevance in semiconductor device engineering  as  SiO2 with its  k= 3.9 was used in both MOS gates and multilevel metallization applications.


Posted by Jerzy Ruzyllo at 04:50 PM | Semiconductors | Link

Sunday, January 4, 2015

#316 “1.24” is a number to remember

Yes, learning should be based primarily on understanding rather than memorization and semiconductor science and engineering is no exception in this regard.


 Still, there are things worth memorizing.  Here is an example concerned with a simple relation converting wavelength of light to energy and vice versa. It comes very handy when interactions of light with semiconductors (absorption, emission, etc.) are of interest.


 It starts with the titans of solid state physics, Max Planck and Albert Einstein and their formulation of a simple relation linking energy E and frequency ν of light E = h ν  where h is a Planck constant. It is enough to recall now that the frequency  ν = c/λ where c is a speed of light in vacuum and  λ the light’s wavelength or the length of the wave of light. So, E (eV)= h c/ λ and with h and c being constants we end up with a convenient formula E (eV)= 1.24/ λ (μm) used to convert wavelength of light to energy and vice versa. Actually, with E~1/λ relation being rather obvious, what needs to be remembered is a proportionality factor 1.24.


Posted by Jerzy Ruzyllo at 08:42 AM | Semiconductors | Link

Tuesday, December 30, 2014

#315 Looking back at 2014

Looking back at the blogs I posted in 2014, I can see that, starting with blog #271, they have touched on a rather eclectic collection of topics.


In retrospect, I would like to point out to the series of six blogs (#281-286) describing interactions of silicon with six elements which are commonly present in the Si device process environment.



Other than that, all the best in 2015! Time is flying….

Posted by Jerzy Ruzyllo at 04:28 PM | Semiconductors | Link

Sunday, December 21, 2014

#314 Atomic Layer Etching, ALE

Atomic Layer Deposition (ALD) took advanced semiconductor manufacturing by storm only some 15 years ago. The ALD turned out to be the best technique for the deposition of a few nm thick high-k gate dielectrics for the 45 nm technology generation CMOS and beyond (see blog #248). Since then, ALD grew into an important tool in the arsenal of thin-film deposition techniques in semiconductor manufacturing with applications expanding beyond just a high-k dielectric deposition.



The success of ALD as an additive process featuring atomic layer precision was not followed by the equally precise, atomic scale, subtractive process. It is because atomic layer-by -atomic layer removal of the material is technically more challenging then equally precise deposition. In contrast to isotropic, conformal AL deposition process, which is mostly independent of the chemical composition of the substrate (ALD creates its own surface chemistry), AL etching needs to be anisotropic and highly selective. Similarly to ALD, however, to accomplish atomic layer precision of the material removal process the ALE reaction should be self-limiting.


Because of these challenges the Atomic Layer Etching (ALE) is coming to the commercial life only now. It is a noteworthy development as with an ALE process complementing ALD processes,  new possibilities in advance semiconductor nano-manufacturing are opening up.


Posted by Jerzy Ruzyllo at 07:24 PM | Semiconductors | Link

Sunday, December 7, 2014

#313 Einstein and semiconductors

The name Albert Einstein is synonymous with the great contributions to theoretical physics. It brings almost instantaneously to mind a theory of relativity which is generally considered as his greatest, or at least the best known, accomplishment.


It was not an accomplishment for which he was awarded a Nobel Prize, however. It was his discovery of the law of the photoelectric effect for which he was recognized with this most coveted prize.


What matters more to the semiconductor community is Einstein’s role in defining fundaments of charge carriers’ kinetics in semiconductors. The relationship between diffusion coefficient and mobility of charge carriers in semiconductor is known as Einstein relationship.


Posted by Jerzy Ruzyllo at 11:13 AM | Semiconductors | Link

Sunday, November 30, 2014

#312 IEDM 2014

Same as during the last 59 years the program of 2014 edition of the IEEE International Electron Device Meeting (IEDM) to be held Dec. 15-17 in San Francisco reflects the current trends in semiconductor science and engineering.


A quick look at the meeting’s program, even just the session titles, is enough to note how fundamentally different it is from its earlier years editions. To follow IEDM’s programs over the years is a good way to monitor the evolution of semiconductor electronics and photonics.


Posted by Jerzy Ruzyllo at 05:53 AM | Semiconductors | Link

Sunday, November 2, 2014

#311 Various shades of CMOS

In some segments of semiconductor community the term CMOS (Complementary Metal-Oxide-Semiconductor) is immediately associable with the digital ICs where it is a MOSFET’s configuration of choice in both logic and memory applications. With unmatched by other types of digital circuitry low power consumption/dissipation, performance as a switch and scalability, CMOS will remain a workhorse of digital electronics for years to come.


Not to disregard is the role CMOS also plays in performing analog functions for instance in operational amplifier ICs and in RF circuitry. Because of its effectiveness in both digital and analog applications, CMOS is a natural choice for the implementation of mixed signal functions which combine digital and analog circuits on the same chip.


What seems to be not as well recognized is the use of CMOS devices for image sensing. Here, CMOS is a lower cost, low-power replacement for the better established CCD (Charge Coupled Devices) image sensors. With inferior to CCD image quality and sensitivity, CMOS imaging devices are the good match for the low-cost, entry level digital cameras.


Frank Wanlass, who invented CMOS in 1963 at Fairchild Semiconductor, very likely did not anticipate such a divers uses for its invention


Posted by Jerzy Ruzyllo at 09:23 PM | Semiconductors | Link

Sunday, October 26, 2014

#310 Recombination means light

The recombination is a physical effect occurring only in semiconductors. It refers to the effect in which electrons from the upper energy band recombine with the holes in the lower energy band and release energy in the process. If a given semiconductor features a direct energy gap then the energy is released mostly as an electromagnetic radiation in the form of a visible light from red to blue range, or invisible infrared light. The operation of all Light Emitting Diodes (LEDs), so ubiquitous these days, is based entirely on this simple principle (strictly speaking the processes leading to the emissive recombination in organic semiconductors are somewhat different than in their inorganic counterparts, but the general idea remains thesame and either way recombination rules… 


I don’t think we fully recognize how profound is our dependence on the process of recombination in semiconductors, so effectively exploited in LEDs. On top on displays, etc., think of LEDs as a source of light in currently virtually all lighting applications.  With life expectancy of just a few month of continuous use and efficiency of about ridiculously low 10%, incandescent bulbs are essentially gone and will never be back. Fluorescent bulbs, including compact fluorescent, are performing better, but will gradually follow incandescent bulbs on the way out as neither in terms of efficiency nor the lifetime they are able to compete with LED-based bulbs.


To make a long story short, whenever and wherever you will see an artificial light, think semiconductors and think recombination.


Posted by Jerzy Ruzyllo at 02:44 PM | Semiconductors | Link

‹‹ ›› is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.

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