Intersection of metallurgy and electronics

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A march for a better world

January 21st 2017 is the day of unity and harmony in support of equity worldwide. As part of our dedication to gender equity, women (and men) of the world have decided to march and as you might have already heard, the march is called “The Women’s March”. As many of women and probably men around the world, I am going to march on January 21st in Melbourne, to send the message that women’s right is human right. However, although this march initially originated with the purpose of supporting women, I believe its universal spread is sending even a larger message to the world beyond gender equity and that is diversity. The beauty and power of this universal march lies in the fact that people of the world are uniting for a common purpose regardless of their origin, gender, colour, sexual orientation or believes. To me, this could be one of the most amazing moments in history in which we are proudly playing a part. 

In this regard, beautiful Sandra Lopez, a women of dedication to high values and standard, has published an inspiring letter to her daughter on why she is going to march. It is highly recommended if you haven’t made your decision yet. I found every single word of her letter resonating with me so deeply that I want to share it here on my blog too. I come from a diverse background in addition to being a woman and very similarly to her, I strongly feel that all the efforts on diversity and gender equity is highly at risk if we don’t act fast. Likewise, I want my kids to live in a better world when they grew up and I do whatever I have in my power to not allow their origin or gender jeopardize their dreams. So I will march in January 21th for a better world. What about you?

Four Steps to Turn Your Idea Into a Business – The Simple Dollar

This post is very useful if you are thinking about having and running your own business. It is worth a read if you need to come up with a decision as to whether or how to turn your idea into business:

http://www.thesimpledollar.com/how-to-turn-your-idea-into-a-business/

How to be more Creative

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As engineers, our core mission is to be creative, right? But we’ve been all there: you are expected to come up with a brilliant idea (for example to improve the designs or processes), but when you sit down to work on it, you don’t get anywhere but dead end. That is when you wonder why you didn’t inherit any of those creative genes 🤔.

There are numerous factors contributing to one leading a flourishing career, but I believe creativity is right at the boarder determining whether we fall into the group of people who potentially flourish or into the group of people who just survive. While there is no need to panic, if you think you don’t have the genes, then there are different strategies for you to kickstart your creativity. Therefore, a better alternative to stressing about that lack of creative genes is to find ways to boost your creativity that works for you 🔎, no matter how disappointing you think of yourself to be. Not every suggested technique in resources works for everybody, but there are a few simple strategies which I found very effective. The point made here is finding ways to make your mind stimulated. That’s the key and here, there are a few simple ways (based on my own personal experiences) listed to keep your mind stimulated.

Get physically active 


There are countless benefits to moderate physical activity and one of them is obviously our creativity.  I have found that during my morning runs, my mind is burst with new ideas no matter which aspect of my life I am focusing on during each run. Luckily, the constructive impact of physical activity on our mind is also backed up by research. So apart from all other benefits, a flourishing career led by your creativity is another reason for you to get active today.

Get out of your comfort zone  


In order for us to be creative, we need to try new things, to see things from different perspectives and to learn to think differently. We need to go far outside of our comfort zone and challenge ourselves regularly. As an example, I found blogging a perfect practice pushing me out of my comfort zone. I have published a post previously on the benefits of blogging to my career but everyone could be different and you might need to find out your own way to keep your mind stimulated. Though remember anything new could appear not your type at first. So unless you don’t try it, you won’t know for sure.

Get artistic 


I know it is not everyone’s type to get artistic but again it is about challenging yourself with something you haven’t done before, in addition to this advantage that ways to get creative with art is limitless. To me, art is very similar to engineering. It is all about skills as well as creativity. Of course we can call ourselves artist when we learn techniques and skills and we employ them to create pieces but that piece won’t turn into a masterpiece unless the element of creativity is incorporated alongside techniques. Having said that, it is your choice as to whether or not to enrol in art classes, but the good thing about getting artistic is that you are still able to get away with not knowing techniques while exploring the boundaries of your creativity. Just remember to take your smartphone everywhere and start taking picture from everything while trying angles, lighting, etc. Alternatively, buy a few bottles of Acrylic paint and a cheap canvas and just start creating. I recommend you starting with abstract painting as you might find it very easy, fun and creative.  

Stay positive 

people are more creative when they are happy.  It is a simple correlation. Staying positive and believing in yourself is an essential element in stimulating your creativity. Staying happy and positive makes it more likly that you’ll be able to think outside of the box and find creative solution. In contrast, when you approach a goal with disbelief, your consequent anxiety clog your thinking, making creativity less probable. Needless to say that the correlation between a positive mindset and creativity is also backed up by research.

what else do you do to stimulate your creativity?   

 

 

Development in electronic packaging and their reliability concerns from metallurgical perspective: part II

As silicon technology continues to advance, engineers have opened up a third dimension (3D ICs) as a viable alternative to the limits of Moore’s law beyond 14 nm technology node. In 3D ICs, TSVs (through silicon vias) are critical elements made of pure copper connecting a multiple stack of dies vertically (Fig below). However, the thermal mismatch between copper and silicon exposes complex stresses in TSV as well as silicon surrounding TSVs leading to Cu extrusion, interfacial failure and performance degradation. In this post, I share with you what I have learnt about the world of TSVs from literature and from metallurgical perspective. I haven’t had the luxury of working in microelectronics industry yet so what it comes in the following is solely originated from my own passion for microelectronics and is rather a general viewpoint. In part I, metallurgy of micro-bumps is discussed.

 

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Fig. 1

Thermal cycling, the trouble-maker

In any physical system consisting of different materials with different thermal expansion coefficient (CTE), residual stresses are inevitable when the entire system is subjected to repeatedly fluctuating temperatures of extreme. Similarly, the mismatch of CTE between Si (CTE: 3ppm/K) and Cu (CTE:17 ppm/K) during processing and service where temperature fluctuates significantly leads to build up of stress in both materials. As a result, the residual stress in copper TSV can easily reach or go beyond its yield stress and this is when important reliability issues emerge.

TSV extrusion:

When temperature rises during processing or service, the rate at which copper expands is much higher than silicon leading to build up of compressive stress in copper TSVs. In response to this compressive stress, copper TSVs pop up at the top where they have the freedom to expand and release the induced stress. Different terms and acronyms created to address the height increase induced by residual stress in copper TSVs, such as “extrusion”, “intrusion”, “pop-up” or “pumping”. Though to prevent confusion, I stick to TSV extrusion in this post. TSV extrusion is in fact caused by plastic deformation of copper and does not go back to its original state when the temperature returns to room temperature.

TSV extrusion is schematically illustrated in Fig 2. The height increase generally is about several hundreds of nanometer which is quite detrimental to BEOL layers above TSVs. TSV extrusion can deform or crack the metal/dielectric stacks on the top, creating serious reliability concerns. In addition, the thermal mismatch of copper and silicon induces stress in silicon, as well, which can potentially influence FEOL, specifically in the region close to the TSV impacting transistors performance. Therefore, a keep-out-zone (KOZ) exists around TSVs to avoid this issue. KOZ is actually a zone free of any devices.

 In order for scientists and engineers to eliminate or lessen the complications associated with residual stresses in TSVs, it is very important that they obtain a systematic understanding of the underlying operating mechanisms in response to residual stress in TSVs. TSVs are made of copper, an FCC crystalline metal, which responses to stresses beyond yield stress based on metallurgical principals. On the other hand, TSVs are in contact with layers of different materials, consequently, interfacial principals have a role to play, as well. Therefore, the issue of TSVs reliability should be approached from two perspectives: 1-metallurgical and 2- interfacial.

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Fig. 2

 

Influence of microstructure on the reliability of TSVs

Generally, when we talk about metallurgy of TSVs in the context of reliability of 3D ICs, grain size and texture as well as impurities are the main factors of consideration. According to Hall-Petch effect, grain size determines the yield strength of a material so that the finer the grain size the stronger the material. Texture is also an important parameter as accumulation of stress within individual grains, as well as deformation mechanisms, can be orientation dependant. Impurities (or second phase particles) are another parameter that captures interest of reliability researchers. To find out the role of these parameters on the reliability of copper TSVs, we need to know about the mechanisms responsible for TSV extrusion, first.

The often discussed mechanisms underlying TSV extrusion are mainly the diffusion based mechanisms such as grain boundary sliding, coble-creep, grain boundary diffusion and lattice diffusion. Although it is not a surprise that at the presence of temperature (originating from BEOL and die-stacking processes or during service) and stress (originating from the thermal mismatch of constituent materials) these mechanisms are easily activated leading to TSV extrusion, preventing activation of these mechanisms entirely might not benefit reliability of TSVs. This is because the stress accumulated within the TSV has to be relaxed somehow and if we don’t allow it to relax through microstructure, it will relax through interface leading to cracks developing at the interface of TSV and barrier layers. Therefore rather than preventing these relaxation mechanisms entirely, the effort should be placed on engineering relaxation mechanisms so that minimum amount of damage occurs. Having said that, there are few researches backing up my above statement in which they have shown that playing with chemistry of electroplating and adding impurities to copper TSV does not benefit reliability issues [1,2]. This is because impurities pin grain boundaries and dislocations and decrease their mobility significantly. This might appear advantageous at first look as it prevents mechanisms responsible for extrusion, but in fact it potentially put the interfaces at a high risk of cracking.

The best possible approach to engineer these relaxation mechanisms could be through controlling grain size and texture. Classically, decreasing grain size increases the strength of metals, however, it should be noted that the easy path of diffusion is through grain boundaries. This means that smaller grain size works in favour of diffusion-based mechanisms. In other words, smaller grain sizes promote larger copper extrusion at the TSV top where there are more freedom for copper to expand in response to fluctuating temperatures and forming stress. Therefore, increasing grain size can technically appear much more beneficial in reducing TSV extrusion. This is consistent with the results of researchers from IMEC where they have shown that microstructure at TSV top in terms of grain size is instrumental and TSV top with single grain show significantly lower extrusion height if compared with TSV top with multiple grains [1,3].

In terms of texture, although there is not a direct correlation between texture and Copper extrusion reported in the literature yet, “bamboo structure” in which grain boundaries are aligned normal to TSV height can be an ideal structure to minimize TSV extrusions. “Bamboo structure” was first introduced to minimize electromigration in TSV copper [4]. The principal associated with “bamboo structure” is that grain boundaries are not directed to the top, therefore, the passages of electrons through grain boundaries to the top is minimised and so is electromigration damage. For the exact same reason, grain boundaries that are not directed to the top of TSV, can reduce diffusion of atoms to the top and consequent TSV extrusion.

Interfacial effects:

In addition to microstructure, Professor Dutta from Washington state university and his research group have done fair amount of research on the interface of TSVs with barrier layers (metallization and passivation layer) and its behaviour in response to residual stresses (for example [5-7]. Based on their work, interface of a metallic material with a non-metallic can be also prone to diffusion and sliding as it can provide an easy path for diffusion of atoms. Therefore similar to microstructure scenario, temperature and stress are driving flux of atoms at the interface (interfacial sliding) assisting the release of residual shear stresses at the interface. It is interesting to know that, interfacial sliding can lead to both TSV extrusion and intrusion depending on the initial state of stress in TSVs [6]. Also, they have investigated the role of electro-migration and found that electric current can enhance extrusion or intrusion if electron flux is in the direction of the shear stress. If not in the same direction, they then counteract each other [5].

[1] J. D. Messemaeker, O. V. Pedreira, H. Philipsen, E. Beyne, I. De Wolf, T. V. Donck & K. Croes, “Correlation between Cu Microstructure and TSV Cu Pumping”, proceeding- Electronic Components & Technology Conference, 2014, 613-619.

[2] T. Jiang et al. “Plasticity mechanism for copper extrusion in through-silicon vias for three- dimensional interconnects”, Applied Physics Letters, 2013, 103, 211906.

[3] I. De Wolf et al. “Cu pumping in TSVs: Effect of pre-CMP thermal budget”, Microelectronics Reliability, 2011, 51, 1856–1859.

[4] R. G. Filippi, J. A. Fitzsimmons,Kevin Kolvenbach, P.-C. Wang, “Electromigration immune through-substrate vias” 2011,US20110193199 A1.

[5] P. Kumar, I. Dutta, “Influence of electric current on diffusionally accommodated sliding at hetero-interfaces” Acta Materialia, 2011, 59, 2096–2108.

[6] P. Kumar, I. Dutta, M. S. Bakir, “Interfacial Effects During Thermal Cycling of Cu-Filled Through-Silicon Vias (TSV)”, Journal of Electronic Materials, 2012, 41, 322-335.

[7] I. Dutta, P. Kumar, M. S. Bakir “Interface-related reliability challenges in 3-D interconnect systems with through-silicon vias”, JOM, 2011, 63, 70-77.

 

 

7 Ways Women Can Thrive In A Male-Dominated Workplace – Forbes

Women of diverse backgrounds have much added difficulties in going up the career ladder and obviously experience higher level of stress in male dominated environments. Although it is a reality of our lives, It is very important that we stay focused rather than distracted by our complex emotions while confronting the stress of working as a double-bind minority. We should take the time to reflect on our situation every now and then to not to lose the sight of our career goals. We should remind ourselves that we are all human with our own vulnerabilities and it is absolutely ok to take the time to stitch ourselves back up if needed. Below article adds a few more to this reminding list:

http://www.forbes.com/sites/amymorin/2016/08/04/7-ways-women-can-thrive-in-a-male-dominated-workplace/#3e31b05d5953

Stress Corrosion Cracking: My New Baby

I recently started to work on a new project related to stress corrosion cracking or in short SCC. For me new projects equal with a lot of happy moments as I have to overcome a lot of challenges initially (needless to say that I belong to that spectrum in which people strive for challenge). One of the challenges is obviously and naturally about learning stuff and based on evidence learning and Serotonin level in my brain are directly linked making me feel happy.

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To show appreciation for the source of my happiness then, I am sharing here some basics about my project and generally SCC, a serious engineering problem intimidating mainly nuclear power, chemical, oil and gas industries. In my case, my project deals with SCC in gas pipeline so I will go through the basics of SCC in gas pipelines.

Interaction of a reactive environment and a susceptible material with tensile stresses lead to crack initiation and growth and eventually (catastrophic) failure. This phenomenon in which three requirements of environment, material and stress has to be met in order for failure to occur is called stress corrosion cracking (SCC). SCC is different from corrosion as in the latter the element of stress is not required for failure to occur. In fact, SCC can occur at instances where varieties of corrosion protection strategies has been applied on the buried energy pipelines. Gas pipelines are manly made of low carbon steel possessing low cost and suitable mechanical properties though with low corrosion resistance. To mitigate the low corrosion resistance, cathodic protection in conjunction with coating is applied. The aim of cathodic protection is to catholically polarize the surface of pipeline in contact with soil. In other words, the surface of the pipeline is covered with electric current (free electrons) converting active metal surface (anodic sites) to passive or cathodic sites. Coating is also applied to further mitigate corrosion by blocking the contact between soil and the pipe surface. However, interestingly enough, application of coating and cathodic protection although preventing one type can lead to another type of damage known as SCC. To explain the mechanism through which the SCC occurs I need to the categorize SCC phenomenon first.

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Another difference between high-PH SCC and near-neutral SCC is the contribution of temperature. In high-PH SCC, temperature has a role to play and that is why high-PH SCC is normally detected immediately downstream of compressor stations where high temperature is more likely. In contrast, near-neutral SCC can be detected well away from the compressor stations, as it is independent of temperature.Generally, there are two types of SCC damage in the gas pipeline system, so-called high-PH SCC and near-neutral SCC. High-PH SCC is a more classical version of SCC in the energy pipelines discovered from mid-1960s while the latter was not documented until mid-1980s (mainly in Canada). In both cases, localized disbondment of the coating is the source of the damage. However in high-PH SCC, the cathodic current reaches the pipeline inside the disbondment while in near-neutral SCC exactly opposite occurs and cathodic current does not reach inside the disbondment because of the shielding effect of the coating or the soil surrounding the pipe. The area under the disbondment could be filled with solutions from the surrounding environment (which act as a corrosive environment on the surface of steel) and whether or not cathodic current reach the solution under disbondment determine the PH of the corrosive environment. Nevertheless, the reaction between the corrosive environment and pipeline steel generates pits and if these generated pits reach to a critical size and depth can act as stress concentration sites leading to crack initiations. The stress required for SCC to occur can be directly applied (hoop stress) or residual in nature (introduced by cold forming, welding, pipe resistance to soil movement, heat treatment, etc).

There are also differences in the mechanisms through which these two types of SCC develops, but I’m not going through that in this post and I might write a separate post around the mechanism later in the future. But a distinct feature in terms of failure analysis is that in high-PH SCC crack normally propagates inter-granular (along grain boundaries) while in near-neutral SCC crack propagates trans-granular (crossing grains).

 

 

It is time to act on gender equality more seroiusly

Recent heartbreaking terrorist attack in Orlando is not merely a result of gun laws in the United States. Don’t take me wrong, I am not supporting the right to possess arms in the US. I am not going to point my finger to Islam either. The problem is not religion related.  The cause of such vast hatred is far more fundamental than passing additional gun control laws or militarized counterterrorism operations to control the hatred acts.

Gender equality is probably not near the top of your list, nor it is something people even think about it when it comes to terrorism  and hatred. But as a matter of fact, research investigating the roots of terrorism have found a strong correlation between terrorism and exclusion and inequality (For example, refer to the work of Caprioli). The role of gender equality in global security and peace is further underscored by UN Security Council resolution 1325 where economic and political empowerment of women worldwide is a foundation to fight against terrorism.

‘Women make up half the world’s population but earn only 10% of the world’s income. This leads to greater vulnerability of women, lower standards of living, inequality and injustice. A direct consequence of which could be raising vulnerable family  with a strong feeling of discrimination and marginalisation. In contrast, empowering women will allow them to have an equal voice with self-confidence providing them with appropriate tools to contribute to a happier, healthier and highly educated family and community. In addition, if women reach their full economic potential, the global economy could benefit up to 12$ trillions by 2025. This potentially reduce  poverty considerably around the globe. Needless to say, poverty, discrimination and marginalisation could be the root cause of  anger and hatred motivating people to commit such devastating acts in the sought of lost happiness and empowerment. it is not to say that all poor or marginalized people will go around killing but the impact of inequality and exclusion is huge and the world cannot afford not to pay attention to it any longer.

Isn’t it really the time to turn the focus of preventing efforts on equality as a precondition to a healthier, prosperous and peaceful world rather than responding hatred with hatred or military strategies?

Culturally Diverse Women in STEMM: Smashing Two Ceilings

Going up the career ladder in science, technology, engineering, mathematics and medicine (STEMM) is indeed hard. Even harder if you are a woman and hardest when you are a woman of diverse background. A significant proportion of graduates in western countries are culturally diverse women, many of them amongst our top performers; but this is […]

http://womeninscienceaust.org/2016/04/21/culturally-diverse-women-in-stemm-smashing-two-ceilings/

Happy International Women’s Day to Men

   

 International women’s day is originally a day to acknowledge the vast range of gender-inequality around the world. During the last couple of days you may have noticed plenty of articles, features and functions in honour of women. As a woman, this makes me really excited as it indicates that the world is waking up to the reality of gender-inequality. However on the other hand, it seems that this waking up is happening to half of humanity – which is women and the other half is far behind in the movement for gender parity. This is mainly because gender-equality is considered as a femenist movemnet and traditionally, feminist movement used to be led by women for women. I don’t believe that it is a feminist move benefiting only women for the reasons I discuss later but even if it was, it should be noted that society performs well when we all work together regardless of gender, race, sexual orientation and ethnic history. As an example of such could be the issue of racism  in the US  where African-American worked together with non-African-American to succeed or the gay rights were granted when gay people had straight people to ally. Similarly, gender-equality movement should be about bringing two halves together. Gender-inequality is not a women’s issue but it is a societal issue that needs both men and women working together. Unless women and men work alongside, we don’t see the transformative change. This is not about men speaking for women or saving them but this is about men supporting women, for the benefit of all. 

Globally, no country has fully attained gender parity yet and but this is not without significance  to note that countries that are affected by social and economical crisis are the ones that are less gender-equal. It is also good to know that studies show that men that live in more gender-equal countries have also a better quality of life with a lower chance of divorce, depression and violence against them.

Gender-equality movement not only benefits women, but also men and children. It is time to rewire our mind and be supportive of the notion that gender-equality is not a femenist cause. The movement needs support from both men and women. The support of the movement could be provided not only in the form advocacy but also in form of contributing to household chores,  caregiving, etc. in an effort to break the stereotypes. Evidence are pilling up that gender-equality leads to better health, happiness and well-being of women, children and men. So there is something in gender-equality conversation for every one. Happy international women’s day to women as well as men.