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By Douglas G. Sutherland and David W. Price

Author’s Note: This is the last in a series of 10 installments that explore certain fundamental truths about process control—defect inspection and metrology—for the semiconductor industry. Each article introduces one of the 10 fundamental truths and highlights its implications. Within this article we will use the term inspection to imply either defect inspection or a parametric measurement such as film thickness or critical dimension (CD).

In the eighth installment1 in this series, “The Tyranny of Numbers,” we discussed the trend of increasing process steps—the number of steps is expected to double between the 20nm and 10nm nodes—and the impact that those additional steps will have on final yield. In addition to impacting yield, the increased complexity of the process flow will also increase production costs and cycle time. As these trends unfold, managing costs and cycle time will become increasingly important to fab operations.

The tenth fundamental truth of process control for the semiconductor IC industry is:

Adding Process Control Reduces Production Costs and Cycle Time

Instrumental to having an efficient, low-cost fab is the ability to collect meaningful information about the process in a timely fashion. Process control tools (metrology and inspection) are the eyes and ears of the fab in that they provide insight into what’s working and what’s not: they are an investment in “process information.” In a 2007 paper2 the National Institute of Standards and Technology (NIST) estimated that the average return on investment for metrology alone was 300 percent.

Previous articles in this series have illustrated how process control can reduce costs by reducing the scrap and raw material costs associated with lost yield and reliability3 failures. Similarly, improving yield reduces the environmental footprint of fab operations per good die out.4 In this article, we will examine two other elements of cost reduction and factory efficiency enabled by process control:

  1. Process equipment re-use from node-to-node
  2. Improved net cycle time

Equipment Re-Use

The single biggest component of cost in a modern fab is capital depreciation. It can vary from company to company, but typically wafer fab capital equipment is depreciated at 20 percent per year over the course of five years. If you can extend the life of a piece of equipment beyond the point where it is fully depreciated you are essentially getting that tool for free. If you can find a way to re-use an entire group of process tools (scanners, etchers, etc.) the savings could easily be measured in tens or even hundreds of millions of dollars.

Ultimately, a process tool must meet the technical specifications that are demanded by the manufacturing process in which it is used. However, in cases where the tool’s capability is marginal, its lifetime can be extended by closer monitoring—using existing metrology or inspection tools to keep the tool operating within the required process specifications. Performing more frequent process tool qualifications can help improve matching and ensure that a tool does not drift out of spec. For stable feed-back and feed-forward schemes, having more in-line inspections provides better averaging and allows for better control of the actual process. In these situations, process control is helping to extend the life of existing process tools—adding process control in this context can actually save money.

The Process Capability Index (Cpk) is a metric that measures how well the natural variation of a process fits within the spec limits. For a centered process with a symmetric distribution the Cpk is given by equation 1,

Cpk = (USL – LSL) / 6σ                             Eq. 1

where USL and LSL are the upper and lower spec limits respectively and s is the standard deviation of the process. If the Cpk value is greater than one, the process is considered capable. Cpk values less than one indicate that the process is not capable.

Consider an etch process step where the Cpk of the CD measurement is exactly equal to one (i.e., the step is marginally capable in that the upper and lower spec limits are both three standard deviations from the mean). The marginal capability could be the fault of the previous photo step, the etch step or both. Either way it is an expensive proposition to upgrade either tool set to improve the Cpk—the capability —of the process.

Often the capability of the process can be improved by implementing a data feed-forward scheme—using additional metrology to fully characterize the process at one step (e.g., photo) and then feeding that information forward to adjust parameters at etch to effectively customize the process conditions for each lot or wafer. Figure 1 below shows an example Statistical Process Control (SPC) chart of the after-etch CD with and without feed-forward.

Figure 1. Left: SPC Chart of etch CD without feed forward (Cpk=1.0). Right: SPC Chart of etch CD with feed forward (Cpk=1.3)

Figure 1. Left: SPC Chart of etch CD without feed forward (Cpk=1.0). Right: SPC Chart of etch CD with feed forward (Cpk=1.3)

Feed-back and feed-forward schemes can be used to extend the useful lifetime of process tools by effectively increasing the process window in which they operate. CD measurements that are slightly off target at photo can be brought back on target by using that information to adjust the etch bias at the etch process step. 

Cycle Time

Cycle time is another very important production metric. We will give a more detailed account of cycle time in an upcoming paper but would like to touch briefly on the counter-intuitive relationship between cycle time and process control.

Any source of variability that prevents lots from moving through the fab in lock-step fashion will increase the cycle time. Adding inspection steps will add cycle time to those lots that get inspected but due to sampling (not every lot gets inspected) it will have a much smaller impact on the average. When an excursion does occur, comparatively few process tools will have to be put down (because the inspection points are closer together) and the module owner will be able to isolate the problem much sooner. The total disruption to the fab (the variability) will be reduced and the cycle time of all lots will be improved. This counter-intuitive concept has been demonstrated by several fabs that have both added inspection steps and reduced cycle time simultaneously.

To summarize, adding process control steps contribute to fab efficiency on several levels (figure 2): increasing baseline yield, extending the useful life of existing process tools, limiting the duration of excursions, and reducing cycle time.

Figure 2. The cascading benefits of process control.

Figure 2. The cascading benefits of process control.

As we conclude this series on the 10 fundamental truths of process control1,3,5-11, we thank you for reading. We hope that these articles have provided deeper insight into the value of process control and the base knowledge for successful implementation of process control in IC fabrication. We look forward to exploring additional aspects of process control in future Process Watch articles throughout the coming months.

References:

About the authors:

Dr. David W. Price is a Senior Director at KLA-Tencor Corp. Dr. Douglas Sutherland is a Principal Scientist at KLA-Tencor Corp. Over the last 10 years, Drs. Price and Sutherland have worked directly with more than 50 semiconductor IC manufacturers to help them optimize their overall inspection strategy to achieve the lowest total cost. This series of articles attempts to summarize some of the universal lessons they have observed through these engagements.

Semico’s Inflection Point Indicator is a model developed by Semico Research, which has a history of accurately predicting semiconductor revenue inflection points four quarters in advance. After analyzing current trends, Semico announced this model indicates the semiconductor industry is repeating the pattern from 2011-2012, albeit at a muted level. Just in the past 4-5 years, the major end markets served by the semiconductor industry–tablets, notebooks, smartphones–have matured, causing growth rates to slow. On top of that, compared to 2012, most of the world’s economies are forecast to be weaker in 2016, with the exception of India. Finally, DRAM prices are expected to be weaker this year, compared to 2012. The positive growth in 2013-2014 was primarily due to the memory shortage and the subsequent rising prices.

Average selling prices (ASPs) in January recovered on lower revenues, which were down 6% year over year. Although ASPs rose 4.0% in January, they are still historically low.

Semico president Jim Feldhan commented, “In the past 8 months, the industry has seen ASPs in the $0.41 range 5 times. One has to go back to May 2009 to find a lower price, and 2009 was not a good year!”

semi ipi

 

The IPI Report is Semico’s most popular report series that accurately predicts semiconductor revenue inflection points four quarters in advance.

SEMI, the global industry association for companies that supply manufacturing technology and materials to the world’s chip makers, today reported that worldwide sales of semiconductor manufacturing equipment totaled $36.53 billion in 2015, representing a year-over-year decrease of 3 percent. 2015 total equipment bookings were 5 percent lower than in 2014. The data are available in the Worldwide Semiconductor Equipment Market Statistics (WWSEMS) Report, now available from SEMI.

Compiled from data submitted by members of SEMI and the Semiconductor Equipment Association of Japan (SEAJ), the Worldwide SEMS Report is a summary of the monthly billings and bookings figures for the global semiconductor equipment industry. The report, which includes data for seven major semiconductor producing regions and 24 product categories, shows worldwide billings totaled $36.53 billion in 2015, compared to $37.50 billion in sales posted in 2015. Categories cover wafer processing, assembly and packaging, test, and other front-end equipment. Other front-end includes mask/reticle manufacturing, wafer manufacturing, and fab facilities equipment.

Spending rates increased for Taiwan, Korea, Japan, and China, while the new equipment markets in North America, Rest of World, and Europe contracted. Taiwan remained the largest market for new semiconductor equipment for the fourth year in a row with $9.64 billion in equipment sales. The expanding markets in South Korea and Japan surpassed the North American market, to claim the second and third largest markets, respectively, while North America fell to fourth place at $5.12 billion. The China market remained larger than the Rest of World and European markets.

The global other front end segment increased 16 percent; the wafer processing equipment market segment decreased 2 percent; total test equipment sales decreased 6 percent; and the assembly and packaging segment decreased 18 percent.

Semiconductor Capital Equipment Market by World Region (2014-2015)

2015

2014

% Change

Taiwan

9.64

9.41

2%

South Korea

7.47

6.84

9%

Japan

5.49

4.18

31%

North America

5.12

8.16

-37%

China

4.90

4.37

12%

Rest of World

1.97

2.15

-9%

Europe

1.94

2.38

-19%

Total

36.53

37.50

-3%

Source: SEMI/SEAJ March 2016; Note: Figures may not add due to rounding.

Chemical precursors (inorganic and organic) used to form high dielectric constant (High-K) materials, metals and metal nitrides needed in advanced ICs are forecasted to reach $400M USD in global sales by 2020, as highlighted in TECHCET’s 2016 Critical Materials Report. Estimated to have totaled over $258M in 2015, this market consists of ~51% high-k metal precursors used for gate dielectrics and capacitors, and ~49% other metal precursors used for electrode and interconnect processes.

The largest usage for High K ALD and CVD (Atomic Layer Deposition and Chemical Vapor Deposition) precursors will continue to be capacitor formation for volatile memory devices through 2020. However, it is expected that revenues for High-K gate oxides processes may surpass memory capacitors by 2021. Compared to CVD, the ALD process relies on unique properties of precursors to self-limit reactions at the atomic level, so ALD precursors are generally chemically engineered complex molecules that command relatively higher average selling prices.

Atomic Layer Etching (ALE) is a new technology similar to ALD, in that alternating sequential surface-limited steps remove precise layers. When engineering atom-scale device features, chip fabricators will continue to rely on such high precision processes employing new and existing materials to enable high quality surfaces. Besides the physical plasma assisted path to ALE employing Cl2 and Ar ions, the chemical path to ALE uses metal organic compounds and hydro fluoric acid, and recent research is focused on using tin(II) acetylacetonate and other beta-diketonates.

Understanding the complex dynamics of materials interactions are critical to the successful use of novel processes and materials in IC HVM. Challenges and opportunities relating to the affordable, controllable, and safe implementation of new materials will be presented in detail at the Critical Materials Conference 2016—open to the public May 5-6, in Hillsboro, Oregon—in conjunction with the private Critical Materials Council (CMC) meetings. For more info on TECHCET’s Report or to Register for the CMC Conference, please go to www.cmcfabs.org/seminars/ or contact [email protected]

TECHCET’s work is focused on process materials supply-chains and materials technology trends for Semiconductor, Display, Solar/PV, and LED manufacturing industries. The company has been responsible for producing the Critical Material Reports for SEMATECH and the industry since 2000. This work continues to benefit the Critical Materials Council, now organized as CMC Fabs. For more info please go to: www.cmcfabs.org or www.techcet.com

Nanoelectronics research center imec has today announced the opening of its new 300mm cleanroom. With this 4000m2 new facility, imec’s semiconductor research cleanrooms now totals 12,000m2, one of the most advanced research facilities in the world dedicated to scaling IC technology beyond 7nm. This facility will enable imec to keep its global leading position as a nanoelectronics R&D center serving the entire semiconductor ecosystem.  Its global partners including foundries, IDMs, fabless and fablite companies, equipment and material suppliers, will benefit from topnotch semiconductor processing equipment (including alfa and beta tools) to develop innovative solutions for more powerful, high-performing, cheaper and energy-efficient ICs, which are crucial in the evolution of the Internet of Everything and a sustainable digital future.

Extending the existing cleanroom, the new facility complies with the newest standards in the semiconductor industry, and provides additional space for the most advanced tools that will lead innovations in new device and system concepts. Installations of the first tools began in January 2016. The new 300mm cleanroom complements imec’s other production facilities including its bio-nanolabs, neuroelectronics labs, imaging and wireless and electronics test labs, photovoltaic pilot lines, and GaN-on-Si, Silicon photonics and MEMS pilot lines.

“Since our founding in 1984, imec has become the world’s largest independent nanoelectronics research center with the highest industry commitment,” stated Luc Van den hove, president and CEO at imec. “This success is the result of the unique combination of our broad international partner network, including the major global players of the semiconductor industry, top scientific and engineering talent, and imec’s one of a kind infrastructure. The extension of our cleanroom provides our partners with the necessary resources for continued leading edge innovation and imec’s success in the future within the local and global high-tech industry.”

The cleanroom was constructed by M+W, an internationally renowned contractor of  large-scale high-tech infrastructure. The construction was completed in 20 months, and includes a  reflecting facade, from Architect Stéphane Beel, which is intended to integrate the building with the environment. The new cleanroom comprises a total investment (building and equipment) of more than 1 billion euro of which 100 million euro funding from the Flemish Government and more than 900 million euro investments from joint R&D with the leading players from the entire semiconductor industry, totaling more than 90 industrial partners.

new imec center

It’s hardly a character flaw, but organic transistors–the kind envisioned for a host of flexible electronics devices–behave less than ideally, or at least not up to the standards set by their rigid, predictable silicon counterparts. When unrecognized, a new study finds, this disparity can lead to gross overestimates of charge-carrier mobility, a property key to the performance of electronic devices.

If measurements fail to account for these divergent behaviors in so-called “organic field-effect transistors” (OFETs), the resulting estimates of how fast electrons or other charge carriers travel in the devices may be more than 10 times too high, report researchers from the National Institute of Standards and Technology (NIST), Wake Forest University and Penn State University. The team’s measurements implicate an overlooked source of electrical resistance as the root of inaccuracies that can inflate estimates of organic semiconductor performance.

A circuit made from organic thin-film transistors is fabricated on a flexible plastic substrate. A team of NIST, Wake Forest, and Penn State University researchers has identified an overlooked source of electrical resistance that can exert a dominant influence on organic-semiconductor performance. Credit: Patrick Mansell/Penn State

A circuit made from organic thin-film transistors is fabricated on a flexible plastic substrate. A team of NIST, Wake Forest, and Penn State University researchers has identified an overlooked source of electrical resistance that can exert a dominant influence on organic-semiconductor performance. Credit: Patrick Mansell/Penn State

Their article appears in the latest issue of Nature Communications.

Already used in light-emitting diodes, or LEDs, electrically conductive polymers and small molecules are being groomed for applications in flexible displays, flat-panel TVs, sensors, “smart” textiles, solar cells and “Internet of Things” applications. Besides flexibility, a key selling point is that the organic devices–sometimes called “plastic electronics”–can be manufactured in large volumes and far more inexpensively than today’s ubiquitous silicon-based devices.

A key sticking point, however, is the challenge of achieving the high levels of charge-carrier mobility that these applications require. In the semiconductor arena, the general rule is that higher mobility is always better, enabling faster, more responsive devices. So chemists have set out to hurry electrons along. Working from a large palette of organic materials, they have been searching for chemicals–alone or in combination–that will up the speed limit in their experimental devices.

Just as for silicon semiconductors, assessments of performance require measurements of current and voltage. In the basic transistor design, a source electrode injects charge into the transistor channel leading to a drain electrode. In between sits a gate electrode that regulates the current in the channel by applying voltage, functioning much like a valve.

Typically, measurements are analyzed according to a longstanding theory for silicon field-effect transistors. Plug in the current and voltage values and the theory can be used to predict properties that determine how well the transistor will perform in a circuit.

Results are rendered as a series of “transfer curves.” Of particular interest in the new study are curves showing how the drain current changes in response to a change in the gate electrode voltage. For devices with ideal behavior, this relationship provides a good measure of how fast charge carriers move through the channel to the drain.

“Organic semiconductors are more prone to non-ideal behavior because the relatively weak intermolecular interactions that make them attractive for low-temperature processing also limit the ability to engineer efficient contacts as one would for state-of-the-art silicon devices,” says electrical engineer David Gundlach, who leads NIST’s Thin Film Electronics Project. “Since there are so many different organic materials under investigation for electronics applications, we decided to step back and do a measurement check on the conventional wisdom.”

Using what Gundlach describes as the semiconductor industry’s “workhorse” measurement methods, the team scrutinized an OFET made of single-crystal rubrene, an organic semiconductor with a molecule shaped a bit like a microscale insect. Their measurements revealed that electrical resistance at the source electrode–the contact point where current is injected into the OFET– significantly influences the subsequent flow of electrons in the transistor channel, and hence the mobility.

In effect, contact resistance at the source electrode creates the equivalent of a second valve that controls the entry of current into the transistor channel. Unaccounted for in the standard theory, this valve can overwhelm the gate–the de facto¬ regulator between the source and drain in a silicon semiconductor transistor–and become the dominant influence on transistor behavior.

At low gate voltages, this contact resistance at the source can overwhelm device operation. Consequently, model-based estimates of charge-carrier mobility in organic semiconductors may be more than 10 times higher than the actual value, the research team reports.

Hardly ideal behavior, but the aim of the study, the researchers write, is to improve “understanding of the source of the non-ideal behavior and its impact on extracted figures of merit,” especially charge-carrier mobility. This knowledge, they add, can inform efforts to develop accurate, comprehensive measurement methods for benchmarking organic semiconductor performance, as well as guide efforts to optimize contact interfaces.

The emerging market for silicon carbide (SiC) and gallium nitride (GaN) power semiconductors is forecast to pass the $1 billion mark in five years, energized by demand from hybrid and electric vehicles, power supplies and photovoltaic (PV) inverters. Worldwide revenue from sales of SiC and GaN power semiconductors is projected to rise to $3.7 billion in 2025, up from just $210 million in 2015, according to IHS Inc. (NYSE: IHS), a global source of critical information and insight. Market revenue is also expected to rise with double digit growth annually for the next decade.

SiC Schottky diodes have been on the market for more than 10 years, with SiC metal-oxide semiconductor field-effect transistors (MOSFET), junction-gate field-effect transistors (JFET) and bipolar junction transistors (BJT) appearing in recent years, according to the latest information from the latest IHS SiC & GaN Power Semiconductors Report. SiC MOSFETs are proving very popular among manufacturers, with several companies are already offering them, and more are expected to in the coming year. The introduction of 900 volt (V) SiC MOSFETs, priced to compete with silicon SuperJunction MOSFETs, as well as increased competition among suppliers, forced average prices to fall in 2015.

“Declining prices will spur faster adoption of the technology,” said Richard Eden, senior market analyst for power semiconductor discretes and modules at IHS Technology. “In contrast, GaN power transistors and GaN modules have only just recently appeared in the market. GaN is a wide bandgap material offering similar performance benefits to SiC, but with greater cost-reduction potential. This price and performance advantage is possible, because GaN power devices can be grown on silicon substrates that are larger and less expensive than SiC. Although GaN transistors are now entering the market, the development of GaN Schottky diodes has virtually stopped.”

By 2020, GaN-on-silicon (Si) devices are expected to achieve price parity with — and the same superior performance as — silicon MOSFETs and insulated-gate bipolar transistors (IGBTs). When this benchmark is reached, the GaN power market is expected to surpass $600 million in 2025. In contrast, the more established SiC power market — mainly consisting of SiC power modules — will hit $3 billion in the same time period.

By 2025, SiC MOSFETs are forecast to generate revenue exceeding $300 million, almost catching Schottky diodes to become the second best-selling SiC discrete power device type. Meanwhile, SiC JFETs and SiC BJTs are each forecast to generate much less revenue than SiC MOSFETs, despite achieving good reliability, price and performance. “While end users now strongly prefer normally-off SiC MOSFETs, so SiC JFETs and BJTs look likely to remain specialized, niche products,” Eden said; “however, the largest revenues are expected to come from hybrid and full SiC power modules.”

Hybrid SiC power modules, combining Si IGBTs and SIC diodes, are estimated to have generated approximately $38 million in sales in 2015 and full SiC power modules are only two or three years behind in the ramp-up cycle. Each module type is forecast to achieve over $1 billion in revenue by 2025.

The IHS SiC & GaN Power Semiconductors Report is based on more than 50 semiconductor supply chain and potential end-user interviews. It provides detailed global analysis of this fast-moving market and explains growth drivers and likely adoption rates in major application sectors.

Total yearly semiconductor unit shipments (integrated circuits and opto-sensor-discrete, or O-S-D, devices) are forecast to continue their upward march and are now expected to top one trillion units for the first time in 2018, according to data presented in IC Insights’ recently released 2016 edition of The McClean Report—A Complete Analysis and Forecast of the Integrated Circuit Industry, and its soon to be released 2016 O-S-D Report—A Market Analysis and Forecast for the Optoelectronics, Sensors/Actuators, and Discretes. Semiconductor shipments in excess of one trillion units are forecast to be the new normal beginning in 2018. Figure 1 shows that semiconductor unit shipments are forecast to climb to 1,022.5 billion devices in 2018 from 32.6 billion in 1978, which amounts to average annual growth of 9.0% over the 40 year period and demonstrates how increasingly dependent on semiconductors the world has become.

The largest annual increase in semiconductor unit growth during the timespan shown was 34% in 1984; the biggest decline was 19% in 2001 following the dot-com bust. The global financial meltdown and ensuing recession caused semiconductor shipments to fall in both 2008 and 2009, the only time the industry has experienced consecutive years in which unit shipments declined. Semiconductor unit growth then surged 25% in 2010, the second-highest growth rate since 1978.

Figure 1

Figure 1

The percentage split of IC and O-S-D devices within total semiconductor units has remained fairly steady despite advances in integrated circuit technology and the blending of functions to reduce chip count within systems. In 1980, O-S-D devices accounted for 78% of semiconductor units and ICs represented 22%. Thirty-five years later in 2015, O-S-D devices accounted for 72% of total semiconductor units, compared to 28% for ICs (Figure 2).

Figure 2

Figure 2

From one year to the next year—and usually depending on the must-have electronic system or product in the market at the time—different semiconductor products emerge to experience the strongest unit shipment growth. Figure 3 shows IC Insights’ forecast of the O-S-D and IC product categories with largest unit growth rates forecast for 2016. Semiconductors showing the strongest unit growth are essential building-block components in smartphones, new automotive electronics systems, and within systems that are helping to build out of Internet of Things. More about these semiconductor products and end-use applications are included in IC Insights’ McClean Report and O-S-D Report.

IC Insights recently released its new Global Wafer Capacity 2016-2020 report that provides in-depth detail, analyses, and forecasts for IC industry capacity by wafer size, by process geometry, by region, and by product type through 2020.  Figure 1 breaks down the world’s installed monthly wafer production capacity by geographic region (or country) as of December 2015.  Each regional number is the total installed monthly capacity of fabs located in that region regardless of the headquarters location for the companies that own the fabs.  For example, the wafer capacity that South Korea-based Samsung has installed in the U.S. is counted in the North America capacity total, not in the South Korea capacity total.  The ROW region consists primarily of Singapore, Israel, and Malaysia, but also includes countries/regions such as Russia, Belarus, Australia, and South America.

Figure 1

Figure 1

Some highlights of regional IC capacity by wafer size are shown below.

As of Dec-2015, Taiwan led all regions/countries in wafer capacity with nearly 22% of worldwide IC capacity installed in the country.  Taiwan surpassed South Korea in 2015 to become the largest capacity holder after having passed Japan in 2011.  China became a larger wafer capacity holder than Europe for the first time in 2010.

For wafers 150mm in diameter and smaller, Japan was the top region in terms of the amount of capacity.  The fabs running small size wafers tend to be older and typically process low-complexity, commodity type products or specialized devices.

The capacity leaders for 200mm wafers were Taiwan and Japan.  There have been many 200mm fabs closed over the past several years, but not in Taiwan and that resulted in the country becoming the largest source of 200mm capacity beginning in 2012.  With Taiwan being home to most of the IC industry’s foundry capacity, the country’s share of 200mm capacity will likely rise further in the coming years.

For 300mm wafers, South Korea was at the forefront, followed by Taiwan.  Taiwan lost its position as the leading supplier of 300mm wafer capacity in 2013.  That was in large part because ProMOS closed its large 300mm fabs, but it was also due to Samsung and SK Hynix continuing to expand their fabs in South Korea to support their high-volume DRAM and flash businesses.

A new one atom-thick flat material that could upstage the wonder material graphene and advance digital technology has been discovered by a physicist at the University of Kentucky working in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece.

Reported in Physical Review B, Rapid Communication, the new material is made up of silicon, boron and nitrogen – all light, inexpensive and earth abundant elements – and is extremely stable, a property many other graphene alternatives lack.

“We used simulations to see if the bonds would break or disintegrate – it didn’t happen,” said Madhu Menon, a physicist in the UK Center for Computational Sciences. “We heated the material up to 1,000 degree Celsius and it still didn’t break.”

Using state-of-the-art theoretical computations, Menon and his collaborators Ernst Richter from Daimler and a former UK Department of Physics and Astronomy post-doctoral research associate, and Antonis Andriotis from IESL, have demonstrated that by combining the three elements, it is possible to obtain a one atom-thick, truly 2D material with properties that can be fine-tuned to suit various applications beyond what is possible with graphene.

While graphene is touted as being the world’s strongest material with many unique properties, it has one downside: it isn’t a semiconductor and therefore disappoints in the digital technology industry. Subsequent search for new 2D semiconducting materials led researchers to a new class of three-layer materials called transition-metal dichalcogenides (TMDCs). TMDCs are mostly semiconductors and can be made into digital processors with greater efficiency than anything possible with silicon. However, these are much bulkier than graphene and made of materials that are not necessarily earth abundant and inexpensive.

Searching for a better option that is light, earth abundant, inexpensive and a semiconductor, the team led by Menon studied different combinations of elements from the first and second row of the Periodic Table.

Although there are many ways to combine silicon, boron and nitrogen to form planar structures, only one specific arrangement of these elements resulted in a stable structure. The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends.

The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. The new material is metallic, but can be made semiconducting easily by attaching other elements on top of the silicon atoms.

The presence of silicon also offers the exciting possibility of seamless integration with the current silicon-based technology, allowing the industry to slowly move away from silicon instead of eliminating it completely, all at once.

“We know that silicon-based technology is reaching its limit because we are putting more and more components together and making electronic processors more and more compact,” Menon said. “But we know that this cannot go on indefinitely; we need smarter materials.”

Furthermore, in addition to creating an electronic band gap, attachment of other elements can also be used to selectively change the band gap values – a key advantage over graphene for solar energy conversion and electronics applications.

Other graphene-like materials have been proposed but lack the strengths of the material discovered by Menon and his team. Silicene, for example, does not have a flat surface and eventually forms a 3D surface. Other materials are highly unstable, some only for a few hours at most.

The bulk of the theoretical calculations required were performed on the computers at the UK Center for Computational Sciences with collaborators Richter and Andriotis directly accessing them through fast networks. Now the team is working in close collaboration with a team led by Mahendra Sunkara of the Conn Center for Renewable Energy Research at University of Louisville to create the material in the lab. The Conn Center team has had close collaborations with Menon on a number of new materials systems where they were able to test his theory with experiments for a number of several new solar materials.

“We are very anxious for this to be made in the lab,” Menon said. “The ultimate test of any theory is experimental verification, so the sooner the better!”

Some of the properties, such as the ability to form various types of nanotubes, are discussed in the paper but Menon expects more to emerge with further study.

“This discovery opens a new chapter in material science by offering new opportunities for researchers to explore functional flexibility and new properties for new applications,” he said. “We can expect some surprises.”