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Sunday, February 16, 2020

#422 Interface

Interfaces are the integral part of any material system comprised of two and more materials in which they typically play the role which defines characteristics of the entire system. As in the case of the surfaces (see previous blog), the effect of an interface between two materials expands into the adjacent regions. An interface is essentially a transition region featuring finite thickness that is needed to allow structural transition between two materials featuring different structure and/or chemical transition between two materials featuring different chemical composition. In either case, interface represents a discontinuity of electrical, optical, mechanical, and thermal properties of the material system.

 

 

From the point of view crystal structure interface is basically a planar defect severely disrupting integrity of the material system, and hence, altering its characteristics. And by the way, the impact of interface on semiconductor device performance manifest itself differently depending onwhether device current is flowing parallel to the interface or across the interface

 

Posted by Jerzy Ruzyllo at 05:45 PM | Semiconductors | Link


Sunday, February 9, 2020

#421 Surface-key element of the material system

In general terms, surface is an exterior face of the solid and represents two-dimensional termination of fundamental characteristics displayed by the three-dimensionally distributed atoms in the bulk of the sample. .In the case of crystals, surface also represents an abrupt discontinuity of crystal structure. In practice, a surface can be significantly disturbed by its roughness (even at the nano-scale) as well as process related physical damage.

 

Considering the above, it is clear that electronic properties of the surface and the near-surface region of any solid, including semiconductors, depart significantly from the same properties in the bulk. For instance, due to the increased scattering of electrons resulting from the defective lattice and electrically charged centers in the near-surface region, transport of electrons close to the surface is significantly disturbed as compared to the transport of electrons in the bulk. This effect has a major adverse effect on the operation of semiconductor devices which depend on the surface and interface related phenomena, e.g., Metal Oxide Semiconductor Field Effect Transistors (MOSFET).

Posted by Jerzy Ruzyllo at 09:41 PM | Semiconductors | Link


Sunday, January 26, 2020

#420 Thirty years ago: January 1990

Following on the previous blog let’s take a quick look at what trends were noticeable in some research papers published exactly 30 years ago.

 

In the January issue of the IEEE Transactions on Electron Device for instance, my attention attracted papers concerned with 2D quantum wells and 2D electron gas. It shows that already thirty years ago quantum phenomena in the highly geometrically confined structures were the subject of thorough exploration. The January issue of the IEEE Electron Device Letters in turn clearly shows that the complex heterostructures involving binary and ternary III-V compounds, and including strained layer superlattices, were pretty common in the advanced research publications at that time.

Posted by Jerzy Ruzyllo at 07:52 PM | Semiconductors | Link


Sunday, January 19, 2020

#419 Thirty years ago

The idea of going back in time to check on what was going on in various engineering domains in the past is not new. As an example, sometime ago IEEE Spectrum published several articles in the series entitled Thirty Years Ago which were analyzing developments in electrical engineering and electronics three decades earlier.  


Look for the future entries on this blog site that will follow the same idea, except that they will be focusing specifically on semiconductors science and engineering. Various   trends emerging thirty years earlier will be identified based on the research papers published in the IEEE and the Electrochemical Society journals.

 

As you will see, it is good to look back in time to remind ourselves that in semiconductor science and engineering, just like in all other areas of engineering sciences, things do not happen overnight and that most of what’s being perceived as new and current is deeply rooted in the work done many years ago.

 

 

Posted by Jerzy Ruzyllo at 01:06 PM | Semiconductors | Link


Sunday, January 12, 2020

#418 Semiconductor material system

 In order to exploit characteristics of semiconductors, complex material systems comprised of elements featuring desired crystal structure and chemical composition need to be created. The elements comprising such complex material systems include surfaces and near-surface regions, interfaces, and thin-films all of which are the integral parts of semiconductor materials systems used to fabricate functional devices and as such have a performance defining effect on such devices.

  

Only in some cases properties of the bulk of semiconductor play the role determining performance of the device. Typically, characteristics of the surface, near surface region and interfaces with other materials forming the device affect the most workings of the devices regardless of whether device is electronic or photonic. And those characteristics depart significantly from the same characteristics (parameters) in the bulk of semiconductor. For instance, due to the increased scattering of charge carriers resulting from the defective lattice and electrically charged centers in the near-surface region, mobility of charge carriers µ close to the surface is reduced significantly as compared to the carrier mobility in the bulk of semiconductor. This effect has a major adverse impact on the semiconductor devices operation of which depends on the surface and interface related phenomena such as for instance Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) which is undeniable “workhorse” of the digital electronics.

 

Posted by Jerzy Ruzyllo at 09:52 AM | Semiconductors | Link


Sunday, December 15, 2019

#417 Defects rule

Considering complexity of the crystal structure of semiconductors (see previous blog),  assumption that they consist of the perfectly periodic three-dimensional arrays of elemental cells, each featuring identical arrangement of atoms over the large volumes of the crystal, is mostly unrealistic.  Real crystals usually contain structural imperfections referred to as defects.  High density of structural defects in semiconductor crystal will prevent its use in the manufacture of high-performance devices because any departures from the lattice periodicity have an adverse effect on electrical characteristics of material, and hence, on the performance of semiconductors devices. 

 

Engineering of the crystals towards minimization of the density of structural defects is a major objective in the processing of single-crystal materials used in the manufacture of semiconductor devices. This is because in the case of high-density of structural defects in the single-crystal semiconductor, the adverse effect of defects will dominate over the intrinsic physical properties of the crystal.

 

Posted by Jerzy Ruzyllo at 09:38 AM | Semiconductors | Link


Sunday, December 1, 2019

#416 Crystallographic order plays key role

The extent to which spatial distribution of atoms in the solid such as silicon for instance is ordered, and what is the geometrical nature of the ensuing crystallographic order defines key electronic characteristics of any given semiconductor material. In terms of crystallographic order two distinct cases are represented by (i) crystals featuring a long-range periodic order and (ii) non-crystalline materials, commonly referred to as amorphous materials in which, in contrast to crystals, atomic arrangement exhibits no periodicity or long-range order.

 

Among crystals, single-crystal and poly-crystalline materials (in some situations also referred to as multicrystalline materials) are distinguished. In the former case, periodic long-range order is maintained throughout the entire piece of material while in the latter case such order is maintained only within the limited in volume grains which are randomly connected to form a solid. An amorphous, non-crystalline material does not feature a long-range order at all and in general features inferior to crystalline materials electronic properties. Don’t this last observation make you conclude that the amorphous materials are of lesser use than crystals. This is not the case because some semiconductor materials are very difficult to obtain in the single-crystal form, yet are broadly used, while some other are used on purpose in the amorphous form because of their lower cost than single-crystals and certain inherent properties which make them especially useful in some applications.

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


Sunday, November 24, 2019

#415 IEDM

This is a time of the year when since the beginning of this blog site its readers are reminded about the IEEE International Electron Device Meeting, IEDM in short, held annually in early December. IEDM is a flagship of the world-wide semiconductor device related conferences and the forum upon which key trends in semiconductor engineering and science are identified and discussed.

 

This year is no exception. The 65th IEDM will be held Dec. 7-11, as usual in San Francisco. You may want to take a look at the program of 2019 IEDM ( https://ieee-iedm.org/program/ ) to see what is happening on semiconductor arena these days.

Posted by Jerzy Ruzyllo at 04:14 PM | Semiconductors | Link


Sunday, November 10, 2019

#414 Some more about substrates

Most commonly, a piece of semiconductor material used to fabricate functional devices is in a form of a thin wafer featuring single-crystal structure and typically thinner than 1 mm. A distinction needs to be made between small and large wafers as well as square/rectangular and circular wafers all with the choice of desired surface orientation. In terms of size, commercial circular wafer substrates can be as small as 20 mm in diameter in the case of some II-VI compound semiconductors, and as large as 450 mm in diameter in the case of silicon wafers.

 

Clearly, while the nature of processes wafers are subjected to in the course of device manufacturing remains the same regardless of the size of the wafer, the way various operations are implemented, and the way wafers are handled, depend on the size and the shape of the wafers. For instance, square, and as thin as some 50 μm Si wafers used in the manufacture of solar cells, where cost of material rather than mechanical stability of the substrate is an issue, are subject to different handling procedures than close to 1000 μm thick, 450 mm in diameter circular Si wafers where mechanical rigidity of the substrate is a prime concern.

Posted by Jerzy Ruzyllo at 10:59 AM | Semiconductors | Link


Sunday, October 27, 2019

#413 A word about substrates

Semiconductor process technology, understood as a technology developed and used for the purpose of manufacturing semiconductor devices, involves complex tools, methods, and procedures devised specifically for semiconductor device fabrication. Semiconductor manufacturing is unique as some devices, for instance cutting edge logic integrated circuits, are among very few mass-produced objects manufactured with truly atomic scale precision.

 

While discussing semiconductor manufacturing processes it is typically assumed that the substrate into which, or onto which devices are built is a rigid semiconductor wafer. What needs to be recognized, however, is that the way various processing step involved in the manufacture of semiconductor devices are implemented depends of the size, shape, degree of flexibility, and chemical makeup of materials used to construct such devices, and commonly referred to as “substrates”.

Posted by Jerzy Ruzyllo at 10:26 AM | Semiconductors | Link


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Semi1source.com/blog 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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