Micro Electro Mechanical Systems MEMS Device Fabrication What

Micro Electro Mechanical Systems (MEMS) Device Fabrication What is a MEM? How are they used? How are they made? What are the challenges encountered during fabrication? EE 4611 04/13/2016 David Niska

Preview MEM applications Fabrication Techniques Lithography Sacrificial layers Micromachining Surface Bulk HAR Material deposition MEM design challenges MEM industry challenges

What is a MEM? Applications • Sensors Sensor Animation Actuators http: //www. sandia. gov/mstc/mems/ http: //electroiq. com/blog/2013/10/mems-devices-for-biomedical-applications/

What’s so special about that? ? Grain of pollen

Device Fabrication Basics Substrate (Si Wafer) Photoresist applied Photoresist masked and exposed Photoresist removal Further processing • Materials etched/dissolved • And/or • Material deposition • Rinse/Repeat http: //www. mdpi. com/1424 -8220/8/9/6077/htm

Keystone Bridge http: //www. keystonefinancialadvisory. com/ http: //www. technologystudent. com/struct 1/arch 1. htm Sacrificial Layers https: //www. studyblue. com/notes/note/n/ancient-etruscan-and-rome-ca 2/deck/15636392

Material Removal (Micromachining) Surface micromachining Bulk micromachining High Aspect Ratio (HAR) http: //www. thinfilmmfg. com/subscribers/Subscriber 02/mems 10 Apr 02. htm Micromachining https: //www. mems-exchange. org/MEMS/fabrication. html

Material Deposition Ø No reactions occur Ø Poly Silicon, Silicon Nitride, Ø chemical Photoresist, glass Silicon Dioxide, metals Ø Similar to frost on a window Spin-on deposition Thermal oxidation Chemical vapor deposition Physical vapor deposition Electroplating http: //chemwiki. ucdavis. edu/@api/deki/files/57994/=figure_2. jpg? revision=1 http: //www 2. ece. gatech. edu/research/labs/vc/theory/oxide. html http: //cnx. org/contents/m 7 vjn. Kh. A@2/Chemical-Vapor-Deposition https: //en. wikibooks. org/wiki/Microtechnology/Additive_Processes https: //www. youtube. com/watch? v=ljb. ESGs 1 Xr. M&list=PLWb. WYEQLb. AEa. N 1 V d. H 9 KF 1 G 3 TPQE 06 Ab. Wd&index=2&nohtml 5=False

Surface micromachining - planar - 2. 5 -d Advantages: • Use existing MOS equipment • Batch Fabrication • Integration with logic components • Silicon has good mechanical properties • Photoresist • Selective etching • Si. O 2 • Sacrificial layers • Insulators • Poly crystalline Si • Structural Layers http: //81. 161. 252. 57/ipci/courses/technology/files/tutorial/images/9/sm 2. gif

Bulk micromachining • Long etching processes • Silicon Nitride used to mask • Wet etching • Isotropic • Anisotropic Isotropic etching Anisotropic etching

HAR (high aspect ratio) Micromachining Deep Reactive Ion Etching (DRIE) LIGA • “Bosch” process • High etching rate • Alternate between etching cycles and passivation cycles • Ions “bombard” the bottom, and not the sides • Both processes use electroplating to build up the final component

Other Types of Micromachining Xenon Difluoride dry phase etching Electro-Discharge micromachining Laser micromachining Focused Ion Beam micromachining

Design Issues/mitigation Examples Stiction Planarization Imaging Interference parts https: //www. google. com/url? sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0 ah. UKEwi 5 raq 4 of. MAh. Wkvo. MKHWf. IBJg. Qj. Rw. IBw&url=http%3 A%2 F%2 Fmemscyclopedia. org%2 Fintro. MEMS. html&psig=AFQj. CNG Gx. Ii 5 -b. VKm. Ac. Qkox 3 hqi. Ye. Vl. NTQ&ust=1460511201959031 https: //www. youtube. com/watch? v=sagm. AHX 4 tcg

Current Industry Challenges Cost Standardization between manufacturers to ensure compatibility Also important for packaging Integration with electronics “system on a chip”

WORKS CITED Alexandre Reis, Raj Bhattacharya. 2004. Deep Reactive Ion Etching (DRIE): https: //ece. umd. edu/class/enee 416. S 2004/report 6. pdf “A (not so) short Introduction to Micro Electromechanical Systems”, F. Chollet, HB. Liu, version 5. 2, 2015: http: //memscyclopedia. org/Document/Intro. MEMS. pdf “MEMS devices for biomedical applications”, Dr. Ramesh Ramadoss, 2013: http: //electroiq. com/blog/2013/10/mems-devices-for-biomedical-applications/ https: //www. mems-exchange. org/MEMS/fabrication. html https: //en. wikipedia. org/wiki/Microelectromechanical_systems#MEMS_basic_processes https: //en. wikipedia. org/wiki/Deep_reactive-ion_etching http: //www. sandia. gov/mstc/mems_info/ https: //www. youtube. com/watch? v=JJEl. LA 8 k 6 Qg&list=PLWb. WYEQLb. AEa. N 1 Vd. H 9 KF 1 G 3 TPQE 06 Ab. Wd&nohtml 5=False https: //www. youtube. com/watch? v=sagm. AHX 4 tcg

5 Key Points Two main applications for mems are sensors and actuators. Isotropic etching attacks a material in all directions, anisotropic etching attacks at different rates in different directions depending on the material’s properties. The three main fabrication techniques are surface micromachining, bulk micromachining, and HAR micromachining. In bulk micromachining, the etching process attacks along the crystalline planes, making orientation of the Si substrate very important. MEMs fabrication differs from MOSFET fabrication mainly by the use of sacrificial layers.