Flexible silicon

Flexible silicon refers to a flexible piece of mono-crystalline silicon. Several processes have been demonstrated in the literature for obtaining flexible silicon from single crystal silicon wafers (either before or after fabrication of CMOS circuits).[1]

Background

According to beam theory and the 3-point test of a rectangular beam of an istoroptic linear material, a perpendicular specific force applied to a rectangular beam would cause it to deflect as a function of its dimension parameters and material properties (i.e. flexural modulus). All parameters fixed, the dependence of the deflection on thickness is inversely proportional, i.e. the thinner the beam the more it deflects when the same force is applied. In a simplistic manner, the applied force per unit area is the stress experienced by the beam. For two beams made of similar materials but one is thinner than the other, a lower force (stress) is required to achieve the same deflection in the thinner beam. This opens up a possibility of reducing a beam's thickness to adjust the amount of stress it can handle before physically breaking, if deflection requirement is the same. Applying this concept on the commonly used brittle Monocrystalline silicon (100) substrates, it can achieve some flexibility (note that silicon is an anisotropic material and requires dealing with elasticity matrix, a tensor, not a simple value for flexural modulus). This is done by using various micro-fabrication techniques and novel approaches to reduce the silicon substrate thickness to few to tens of micrometers, enabling bending up to 0.5 cm radius without breaking.

Processes

Etch protect release approach and backside etch are few examples of how this can be achieved. These techniques have been extensively used to demonstrate flexible versions of traditional high-performance CMOS compatible devices, including 3D fin-field effect transistors (finFETs)[2][3] and planar metal-oxide-semiconductor FETs (MOSFETs),[4] metal-oxide semiconductor/metal-insulator-metal capacitors (MOSCAPs and MIMCAPs),[5][6][7] ferroelectric capacitors and resistive devices,[8][9][10][11] and thermoelectric generators (TEGs).[12]

References
  1. Hussain, Aftab M.; Hussain, Muhammad M. (June 2016). "CMOS-Technology-Enabled Flexible and Stretchable Electronics for Internet of Everything Applications". Advanced Materials. 28 (22): 4219–4249. doi:10.1002/adma.201504236. PMID 26607553.
  2. Ghoneim, Mohamed; Alfaraj, Nasir; Torres-Sevilla, Galo; Fahad, Hossain; Hussain, Muhammad (July 2016). "Out-of-Plane Strain Effects on Physically Flexible FinFET CMOS". IEEE Transactions on Electron Devices. 63 (7): 2657–2664. doi:10.1109/TED.2016.2561239. hdl:10754/610712.
  3. Torres Sevilla, Galo A; Ghoneim, Mohamed T; Fahad, Hossain; Rojas, Jhonathan P; Hussain, Aftab M; Hussain, Muhammad M (5 September 2014). "Flexible nanoscale high-performance FinFETs". ACS Nano. 8 (10): 9850–6. doi:10.1021/nn5041608. PMID 25185112.
  4. Rojas, Jhonathan P; Torres Sevilla, Galo A; Hussain, Muhammad M (10 September 2013). "Can we build a truly high performance computer which is flexible and transparent?". Scientific Reports. 3: 2609. doi:10.1038/srep02609. PMC 3767948. PMID 24018904.
  5. Ghoneim, Mohamed T.; Rojas, Jhonathan P.; Young, Chadwin D.; Bersuker, Gennadi; Hussain, Muhammad M. (26 November 2014). "Electrical Analysis of High Dielectric Constant Insulator and Metal Gate Metal Oxide Semiconductor Capacitors on Flexible Bulk Mono-Crystalline Silicon". IEEE Transactions on Reliability. 64 (2): 579–585. doi:10.1109/TR.2014.2371054.
  6. Ghoneim, Mohamed T.; Kutbee, Arwa; Ghodsi, Farzan; Bersuker, G.; Hussain, Muhammad M. (9 June 2014). "Mechanical anomaly impact on metal-oxide-semiconductor capacitors on flexible silicon fabric". Applied Physics Letters. 104 (23): 234104. doi:10.1063/1.4882647. hdl:10754/552155.
  7. Rojas, Jhonathan P; Ghoneim, Mohamed T; Young, Chadwin D; Hussain, Muhammad M (October 2013). "Flexible High-k Metal Gate Metal/Insulator/Metal Capacitors on Silicon (100) Fabric". IEEE Transactions on Electron Devices. 60 (10): 3305–3309. doi:10.1109/TED.2013.2278186.
  8. Ghoneim, Mohamed T.; Hussain, Muhammad M. (23 July 2015). "Review on physically flexible nonvolatile memory for internet of everything electronics". Electronics. 4 (3): 424–479. arXiv:1606.08404. doi:10.3390/electronics4030424.
  9. Ghoneim, Mohamed T.; Hussain, Muhammad M. (3 August 2015). "Study of harsh environment operation of flexible ferroelectric memory integrated with PZT and silicon fabric". Applied Physics Letters. 107 (5): 052904. doi:10.1063/1.4927913. hdl:10754/565819.
  10. Ghoneim, Mohamed T.; Zidan, Mohammed A.; Alnassar, Mohammed Y.; Hanna, Amir N.; Kosel, Jurgen; Salama, Khaled N.; Hussain, Muhammad (15 June 2015). "Flexible Electronics: Thin PZT-Based Ferroelectric Capacitors on Flexible Silicon for Nonvolatile Memory Applications". Advanced Electronic Materials. 1 (6): 1500045. doi:10.1002/aelm.201500045.
  11. Ghoneim, Mohamed T; Zidan, Mohammed A; Salama, Khaled N; Hussain, Muhammad M (30 November 2014). "Towards neuromorphic electronics: Memristors on foldable silicon fabric". Microelectronics Journal. 45 (11): 1392–1395. doi:10.1016/j.mejo.2014.07.011.
  12. Torres Sevilla, Galo; Bin Inayat, Salman; Rojas, Jhonathan; Hussain, Aftab; Hussain, Muhammad (9 December 2013). "Flexible and Semi‐Transparent Thermoelectric Energy Harvesters from Low Cost Bulk Silicon (100)". Small. 9 (23): 3916–3921. doi:10.1002/smll.201301025. PMID 23836675.
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