Reliability of flexible and stretchable electronics is a key area to explore. Specially their usage are intended to be mostly for wearable and implantable electronics applications. In both cases, their functionality and longevity will depend on individual user. Plus implantable electronics need to have near "infinite" lifetime. From these perspectives, it is critical to study reliability science of such emerging electronics where mechanical deformation will play critical role. And hence, we frequently explore and introduce new reliability metrics.

What is cumulative impact budget? Why reversibly bi-stable material can be useful for flexible electronics?

Flexibility can bring a new dimension to state-of-the-art electronics, such as rollable displays and integrated circuit systems being transformed into more powerful resources. Flexible electronics are typically hosted on polymeric substrates. Such substrates can be bent and rolled up, but cannot be independently fixed at the rigid perpendicular position necessary to realize rollable display-integrated gadgets and electronics. A reversibly bistable material can assume two stable states in a reversible way: flexibly rolled state and independently unbent state. Such materials are used in cycling and biking safety wristbands and a variety of ankle bracelets for orthopedic healthcare. They are often wrapped around an object with high impulsive force loading. Here, we study the effects of cumulative impulsive force loading on thinned (25 μm) flexible silicon-based n-channel metal–oxide–semiconductor field-effect transistor devices housed on a reversibly bistable flexible platform. We found that the transistors have maintained their high performance level up to an accumulated 180 kN of impact force loading. The gate dielectric layers have maintained their reliability, which is evidenced by the low leakage current densities. Also, we observed low variation in the effective electron mobility values, which manifests that the device channels have maintained their carrier transport properties.

This paper introduced for the first time the concept of cumulative budget impact and also studied reversibly bi-stable material (like safety braces for bikers) that can be used as the host substrate for flexible display technology

  1. N. Alfaraj, A. M. Hussain, G. A. Torres Sevilla, M. T. Ghoneim, J. P. Rojas, A. B. Aljedaani, M. M. Hussain, “Functional integrity of flexible n-channel metal─oxide─semiconductor field-effect transistors on a reversibly bistable platform, Appl. Phys. Lett. 107, 174101 (2015). [Cover Page and Feature Article] [Top Paper 2015 – Editor’s Pick]
  2. M. T. Ghoneim, J. P. Rojas, C. D. Young, G. Bersuker, M. M. Hussain, “Electrical analysis of high-κ/metal gate metal oxide semiconductor capacitors on flexible bulk mono-crystalline silicon (100)”, IEEE Trans. Reliab. 64(2), 579-585 (2015).
  3. M. T. Ghoneim, A. Kutbee, F. Ghodsi Nasseri, G. Bersuker, M. M. Hussain, “Mechanical Anomaly Impact on Metal-Oxide-Semiconductor Capacitors on Flexible Silicon Fabric”, Appl. Phys. Lett. 104, 234104 (2014).

What happens to high performance non-planar FinFET CMOS electronics when they are flexible and under severe mechanical deformation?

We are the only research lab in the world who have demonstrated flexible version of the state-of-the-art FinFET CMOS. Leveraging such advances, we have extensively studied its behavior under severe mechanical deformation.

We presented a comprehensive electrical performance assessment of hafnium silicate (HfSiOx) high-κ dielectric and titanium-nitride (TiN) metal-gate-integrated FinFET-based complementary-metal-oxide-semiconductor (CMOS) on flexible silicon on insulator. The devices were fabricated using the stateof-the-art CMOS technology and then transformed into flexible form by using a CMOS-compatible maskless deep reactive-ion etching technique. Mechanical out-of-plane stresses (compressive and tensile) were applied along and across the transistor channel lengths through a bending range of 0.5-5 cm radii for n-type and p-type FinFETs. Electrical measurements were carried out before and after bending, and all the bending measurements were taken in the actual flexed (bent) state to avoid relaxation and stress recovery. Global stress from substrate bending affects the devices in different ways compared with the well-studied uniaxial/biaxial localized strain. The global stress is dependent on the type of channel charge carriers, the orientation of the bending axis, and the physical gate length of the device. We, therefore, outline useful insights on the design strategies of flexible FinFETs in future free-form electronic applications.

  1. M. T. Ghoneim, N. Alfaraj, G. A. Torres Sevilla, H. M. Fahad, M. M. Hussain*, “Out-of-Plane Strain Effects on Physically Flexible FinFET CMOS”, IEEE Trans. Elect. Dev. 63(7), 2657–2664 (2016).
  2. A. Diab, G. Torres Sevilla, S. Cristoloveanu, M. M. Hussain*, “Room to High Temperature Measurements of Flexible SOI FinFETs with Sub-20 nm Fins”, IEEE Trans. Elect. Dev. 61(12), 3978-3984 (2014).

In addition to flexibility, what other interesting advantages our trench-protect-peel-reuse process offers?

Lets think the difference between MacBook Air vs. MacBook Pro. The former is lighter than the later but the later offers more performance. The reason is additional heat management utilities to manage additional heats dissipated by additional number of chips which are allowing this performance enhancement in MacBook Pro. Our study conclusively shows that our trench-protect-peel-reuse process allows not only flexibility but also the generated porosity let the air to flow within the thinned silicon body. Not only loosing weight but also like human brain cooling by air flown through nostril.

  1. M. T. Ghoneim, H. M. Fahad, A. M. Hussain, J. P. Rojas, G. A.Torres Sevilla, N. Alfaraj, E. B. Lizardo, M. M. Hussain*, “Enhanced cooling in mono-crystalline ultra-thin silicon by embedded micro-air channels”, AIP Adv. 5, 127115 (2015).
  2. M. T. Ghoneim, J. P. Rojas, A. M. Hussain, M. M. Hussain*, “Additive advantage in characteristics of MIMCAPs on flexible silicon (100) fabric with release-first process” Phys. Status Solidi (RRL) 8(2) 1–4 (2013).

How do the flexible and stretchable electronics perform under harsh environment?

We have studied both high performance flexible logic and memory devices. Our study on physical-mechanical-electrical characteristics of a flexible ferroelectric memory based on lead zirconium titanate as a key memory material showed a bending radius down to 1.25 cm corresponding to 0.16% nominal strain (high pressure of ∼260 MPa), and full functionality up to 225 °C high temperature in ambient gas composition (21% oxygen and 55% relative humidity). The devices showed unaltered data retention and fatigue properties under harsh conditions, still the reduced memory window (20% difference between switching and non-switching currents at 225 °C) requires sensitive sense circuitry for proper functionality and is the limiting factor preventing operation at higher temperatures.

We also studied on high temperature electrical transport characteristics of a flexible version of the semiconductor industry's most advanced architecture: fin field-effect transistor on silicon-on-insulator with sub-20 nm fins and high-κ/metal gate stacks. Characterization from room to high temperature (150 °C) was completed to determine temperature dependence of drain current (Ids), gate leakage current (Igs), transconductance (gm), and extracted low-field mobility(μ0). Mobility degradation with temperature is mainly caused by phononscattering. The other device characteristics show insignificant difference at high temperature which proves the suitability of inorganic flexible electronics with advanced device architecture.

  1. M. T. Ghoneim, M. M. Hussain, “Study of harsh environment operation of flexible ferroelectric memory integrated with PZT and silicon fabric”, Appl. Phys. Lett. 107, 052904 (2015).
  2. A. Diab, G. A. Torres Sevilla, M. T. Ghoneim, M. M. Hussain, “High Temperature Study of Flexible Silicon-On-Insulator Fin Field-Effect Transistors”, Appl. Phys. Lett. 105, 133509 (2014).

Are paper electronics reliable?

Its a tricky question. First, paper has been in use for hundreds of years. Second, paper is a Technology Readiness Level (TRL) 7 materials. Specially, we are the only group who use non-functionalized papers (which one can easily obtain from the kitchen). We have studied the bending mechanics and reliability under various physical deformation of paper electronics and find remarkable resilience. Obviously any paper is subjected to wear, tear, aging, burning and wetting and thus appropriate encapsulation is necessary.

In our study, we showed the general mechanical properties of the cellulose paper used and its electrical behavior under applied strain, tackling the main effects that need to be identified when building paper-based systems, from product performance and stability perspective. An overview of the stress-strain behavior of silver ink on paper is discussed, and then, we tackle a more specific analysis of the performance variations of paper sensors made with recyclable household materials when exposed to various mechanical conditions of tensile and compressive bending. This paper is important for developing stable wearable sensors for incorporation into Internet of Everything applications.

J. M. Nassar, M. M. Hussain*, “Impact of Physical Deformation on Electrical Performance of Paper-based Sensors”, IEEE Trans. Elect. Dev. 99, 1–8 (2017)