Mặt nạ sau khi được thiết kế trong phần mềm L-Edit gồm rất nhiều các thiết kế micromotor (tương ứng với mỗi chip) sẽđược gửi đi để tạo mặt nạ chủ thực hiện cho quy trình gia công. Dưới đây là hình ảnh mặt nạđược thiết kế trong phần mềm L-Edit.
KẾT LUẬN
NGUYỄN ĐÌNH HƯỚNG 70
KẾT LUẬN
Với đề tài tốt nghiệp: “Thiết kế cải tiến và lập quy trình chế tạo micromotor
quay dựa trên công nghệ MEMS”, tác giả đã hoàn thành luận văn với những kết
quả như sau.
Luận văn đã phân tích một số loại micromotor hoạt động dựa trên hiệu ứng tĩnh điện. Đặc biệt là kiểu micromotor quay đã được đề xuất bởi tác giả Phạm Hồng Phúc[4]. Hệ thống này được dẫn động bởi bốn bộ kích hoạt răng lược cong hoạt
động dựa trên hiệu ứng tĩnh điện. Điện áp xoay chiều được cấp vào bộ kích hoạt sẽ
biến chuyển động lắc của phần răng cóc thành chuyển động quay một chiều của vành răng cóc micromotor. Tuy nhiên, khi hoạt động ở tần số cao thì xảy ra hiện tượng trượt giữa các răng cóc dẫn và vành răng cóc. Để khắc phục hiện tượng này, luận văn đã đề xuất ra hai phương án cải tiến ở phần dẫn động để hệ thống có thể
làm việc được ở dải vận tốc lớn hơn. Phân tích lực trong hệ thống truyền động cũng
được đề cập để thiết lập mối tương quan giữa lực đàn hồi cổ dầm và lực nén lò xo. Thông qua chuyển vị cần thiết của răng cóc dẫn, ta sẽ tính toán được áp lực tác dụng lên các răng cóc đó trong quá trình dầm trở về vị trí ban đầu. Áp lực này cần phải thắng được lực đẩy của lò xo để các răng cóc dẫn có thể trượt về vị trí ban đầu. Phần mô phỏng tính toán sử dụng phần mềm phần tử hữu hạn ANSYS. Thông qua các kết quả chuyển vị, ứng suất thu được để lựa chọn kích thước tối ưu cho micromotor.
Cuối cùng, luận văn đã đề xuất một quy trình gia công micromotor sử dụng công nghệ gia công sâu (bulk-micromachining) chỉ cần một mặt nạ. Hệ thống micromotor được thiết kế, chế tạo trên phiến SOI (silicon trên lớp cách điện) với các quy trình công nghệ cơ bản như: quy trình quang khắc (Photolithography), quy trình ăn mòn ion hoạt hóa sâu (D-RIE), và quy trình ăn mòn bằng hơi axit HF (Vapor HF Etching).
KẾT LUẬN
NGUYỄN ĐÌNH HƯỚNG 71
Ưu điểm của micromotor loại này là kích thước gọn, đơn giản trong gia công và điều khiển, đạt độ chính xác cao vì chỉ sử dụng một mặt nạ chủ.
Với những kết quả đạt được, trong tương lai, ta có thể sử dụng chuyển động quay của micromotor này cho các bộ truyền động bánh răng siêu nhỏ trong các micro robot. Ngoài ra, ta có thể sử dụng micromotor này cho các thiết bị dẫn động chính xác nhưđồng hồ siêu nhỏ (micro clock). Khi đó, tần số của điện áp đặt vào bộ
TÀI LIỆU THAM KHẢO
NGUYỄN ĐÌNH HƯỚNG 72
TÀI LIỆU THAM KHẢO
1. Pham Hong Phuc, (2007), “Study on Micro Transportation Systems Based on Electrostatic Actuators Utilizing Micro Electro Mechanical Systems (MEMS) Technology”,Ph.D Thesis, Ritsumeikan University, Japan.
2. Pham Hong Phuc, Dao Viet Dung, Satoshi Amaya, Ryoji Kitada and Susumu Sugiyama, (2006), “Straight movement of micro containers based on ratchet mechanisms and electrostatic comb-drive actuators”, Journal of Micromechanics and Microengineering, vol 16, p2532- 2538.
3. Pham Hong Phuc, Dao Viet Dung, Satoshi Amaya, (2007), “A micro transportation system (MTS) with large movement of containers driven by electrostatic comb-drive actuators”, Journal of Micromechanics and Microengineering, vol 17, p2125- 2131.
4. Pham Hong Phuc, Dao Viet Dung, Bui Thanh Tung, Susumu Sugiyama, (2008), “A micro rotational motor based on ratchet mechanism and electrostatic comb – drive actuators”, Apcot, Tainan, Taiwan.
5. Je’ne’mie Bouchaud, Director and Principal Analyst and Richard Dixon, Senior Analyst, (2009), “Economic Crisis Accelerates Transformation of the MEMS Industry”, MEMS market tracker- iSupply.
6. Gregory T.A.Kovacs, (1998), Micromachined Transducers Source Book,
Stanford University, p276-303.
7. Gregory T.A.Kovacs, member, IEEE, Nadim I.Maluf, member, IEEE, and Kurt E.petersen, fellow, IEEE, (1998), “Bulk Micromachining of Silicon”,
The Proceedings of the IEEE, vol.86, No.8.
8. Gijs Krijnen, NielsTas, “Micromechanical Actuators”, MESA and Research Institute, Transducer Technology Laboratory, University of Twente, Enschede, The Netherlands.
TÀI LIỆU THAM KHẢO
NGUYỄN ĐÌNH HƯỚNG 73
9. Nicolae Lobontiu Ephrahim Garcia, (2005), “Mechanics of Microelectromechanical Systems”, Kluwer Academic Publishers, Boston. 10.Rob Legtenberg, (1996), “Comb- drive actuators for large displacements”,
MESA Reseach Institude, Univesity of Twente, PO Box 217, 7500 AE Enschede, The Netherlands.
11.Sami Franssila, (2004), “Introduction to Microfabrication”, Director of Microelectronics Centre, Helsinki University of Technology, Finland.
12.Stephen M. Barnes, Samuel L. Miller, M. Steven Rodgers, Fernando Bitsie, (2000), “Torsional Ratcheting Actuating System”, Sandia National Laboratories, MS 1080, PO Box 5800, Albuquerque, NM, 87185.
13.Tang W C, Nguyen T H and Howe R T ,(1989), “Laterally Driven Polysilicon Resonant Microstructures”, Tech. Dig. IEEE Micro Electro Mech. Syst Workshop (1989), pp 53-59.
14.Tang W C, Nguyen T H, Michael W J and Howe R T, (1990), “Electrostatic- comb Drive of Lateral Polysilicon Resonators”, Sensors and Actuators A21- A23 (1990), pp 328-331.
15.Đinh Bá Trụ, Hoàng Văn Lợi, (2003), Hướng dẫn sử dụng Ansys, Hà Nội. 16. Nguyễn Việt Hùng, Nguyễn Trọng Giảng, (2003), Ansys và mô phỏng số
trong công nghiệp phần tử hữu hạn, NXB Khoa học và kỹ thuật, Hà Nội. 17. Kent L. Lawrence, (2006), Ansys workbench Tutorial ANSYS Release 10,
PHỤ LỤC
NGUYỄN ĐÌNH HƯỚNG 74
PHỤ LỤC
1. Bài báo của của tác giả Phạm Hồng Phúc và các đồng nghiệp tại hội nghị
APCOT- 2008
- - -
A MICRO ROTATIONAL MOTOR BASED ON RATCHET MECHANISM AND ELECTROSTATIC COMB-DRIVE ACTUATORS
Phuc Hong Pham, Dzung Viet Dao, Tung Thanh Bui and Susumu Sugiyama
Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
ABSTRACT
This paper presents design and fabrication of a Micro Rotational Motor (MRM) that utilizes four silicon electrostatic comb-drive actuators to drive a ring (or rotor) through ratchet teeth. Novelty design of anti-reverse structure overcomes the gap problem after deep reactive ion etching of silicon. The MRS has been fabricated by using SOI wafer with device layer of 30µm and tested for performance. It was driven by periodic voltage (Vpp = 80V) with different frequencies from 1Hz to 30Hz. In this range, the angular velocity of the ratchet ring was proportional with the frequency and matched very well with theoretical calculation.
Keywords: Micro rotational motor (MRM), Rotational comb actuator, Ratchet ring.
1. INTRODUCTION
Micro electrostatic comb-drive actuators and applications are important components in MEMS. Since the first reports on micromachined comb actuator by Tang et al [1, 2], there have been substantial researches on comb-drive actuators both theory and applications. Electrostatic effect of comb actuators were well investigated analytically [3]. In [4, 5], research on micromachined comb actuator focuses on the structure design to obtain large displacement and high stability. Comb actuators have been used in many applications, such as optical switches [6], as a driver for micro gear trains [7, 8] or move the shuttle forward in the linear inchworm motor [9].
The design and fabrication of micro rotary motor has been a topic of many recent publications. Sniegowski et al. used two sets of linear comb actuators to drive the output gear [7, 8]. The linear motion of comb actuator has been converted to rotary motion via linkages pinned into the output gear. Kim developed a rotary motor by inchworm motion. A rotor is wrapped by two opposite belts which are connected to piezoelectric actuators [10]. Sammoura demonstrated a rotary inchworm motor using four gap-closing actuators to rotate a free moving rotor [11]. Advantages of these types are high angular velocity and low driving voltage. However they required sophisticated control systems.
Fig. 1: Configuration of the micro rotational motor (MRM)
In this paper, the electrostatic comb-drive actuator will be used to drive a micro rotational
PHỤ LỤC
NGUYỄN ĐÌNH HƯỚNG 75
motor (MRM) through ratchet mechanism. The micro ratchet was first used in MEMS by Sandia National Laboratories [12, 13] and by the authors [14]. The advantages of this MRM are batch fabrication, simple configuration and control.
2. CONFIGURATION AND
WORKING PRINCIPLE OF THE MRM
Figure 1 shows one module of the MRM, which consists of four rotational comb actuators, four anti- reverse mechanisms and outer ratchet ring. Ratchet ring can rotate in one direction due to reciprocal motion of the rotational comb actuators through ratchet teeth and anti-reverse mechanism.
Structure of the rotational comb actuator is shown in Fig. 2. The rotational comb actuator here refers to the electrostatic comb-drive actuator that the movement of its fingers is rotational around an elastic point (enlargement at the bottom in Fig. 2). Ratchet rack, with suitably shaped teeth as saw teeth, connected with movable comb fingers through spring, can drive the outer ratchet ring in one direction and allow ‘free-sliding’ between them in the reverse direction (enlargement at the top in Fig. 2). The pitch and height of a ratchet tooth are 10µm and 6µm, respectively, (Fig. 3).
Configuration of anti-reverse mechanism is shown in Fig. 4. A minimum gap of 2µm between the tip of the anti-reverse hair and the nearest tooth of the rotor ring is necessary for Deep-RIE (reactive ion etching) process. However, this gap must be eliminated when the motor is working. The anti-gap lever is designed for this purpose. When it is pushed to the lock position, its tip will hit on the anti-reverse hair, and makes it bent outward so that the hair's tip touches to the tooth of the rotor ring to create a ratchet mechanism. This allows the rotor ring rotates in only one direction.
When the ratchet rack moves to the right, it pushes the ratchet ring (or rotor ring) to the right. When voltage decreases to zero, the spring will be compressed and the ratchet rack returns to initial position with a sliding occurs between its teeth and the ratchet teeth of the rotor ring. The rotor ring can not go back due to the anti-reverse mechanisms (Fig. 4). After each motion cycle of rotational comb actuator, the teeth of ratchet ring rotate by n×pitch. The pitch and height of the ratchet teeth are 10µm and 6µm, respectively. The integer number n = 1, 2,
etc. depends on displacement of driving ratchet rack, and therefore, on the amplitude of driving voltage.
Fig. 2: Rotational comb actuator structure.
Fig. 3: Dimensions of ratchet rack and teeth.
Fig. 4: Configuration of anti-reverse mechanism.
3. FABRICATION AND TEST
The fabrication process is illustrated in fig. 5. The MRM has been fabricated by using SOI wafer with the thicknesses of device layer, buried SiO2 layer, and silicon substrate were 30µm, 4µm and 500µm, respectively, (fig. 5(a)). Firstly, the mask was designed and used for photolithography process. The MRM patterns were transferred to the surface of SOI wafer after photolithography and developing, (fig. 5(b)). Secondly, D-RIE process was performed to a depth of 30µm to reach the buried oxide layer, the rate of D-RIE is about 1.2µm/minute, (fig. 5(c)). Then, silicon wafer is diced to separate each MRM. Next, photoresist layer on the device surface is removed by remover solution, and then vapor HF
PHỤ LỤC
NGUYỄN ĐÌNH HƯỚNG
etching process was done to etch the SiO underneath the device layer and release the movable electrodes, (fig. 5(d)). Vapor HF etching is the key technique here to overcome the sticking problem, which is most frequently occurred in fabrication of silicon comb actuators. The etching rate of SiO vapor HF with concentration of 46% at 40 0.2µm/minute. After HF etching, the actuator structure is dried at 120°C for 10 minutes to further reduce the sticking problem. The silicon MRM and its components after fabrication are shown in figures 6.
Fix 5: Fabrication process: (a) SOI wafer, (b) Photolithography, (c) D-RIE, (d) Vapor HF etching.
Fig. 6: SEM image of MRM and its components
a) Before insertion of anti
NG 76
etching process was done to etch the SiO2
nderneath the device layer and release the movable electrodes, (fig. 5(d)). Vapor HF etching is the key technique here to overcome the sticking problem, which is most frequently occurred in fabrication of silicon comb actuators. The etching rate of SiO2 by vapor HF with concentration of 46% at 40°C is m/minute. After HF etching, the actuator C for 10 minutes to further reduce the sticking problem. The silicon MRM and its components after fabrication are shown in figures
Fix 5: Fabrication process: (a) SOI wafer, (b) RIE, (d) Vapor HF etching.
Fig. 6: SEM image of MRM and its components
a) Before insertion of anti-gap lever
(b)After insertion of anti
Fig. 7: SEM image of the anti-reverse mechanism
Figure 7 shows the structure of anti mechanism. In fig. 7 (a), the anti
the initial position, while in fig. 7 (b), the anti lever is pushed into working position, i.e. locked position. Note that, the 2µm-gap was eliminated in fig. 7 (b).
Finally, the rotational electrostatic motor has been tested for performance. They were driven by periodic voltage (Vpp = 80V) with different frequencies from 1Hz to 30Hz. When driving frequency was lower than 20Hz, the angular velocity of the ratchet ring was proportional with the frequency and matched very well with theoretical calculation. Beyond this range, the angular velocity was saturated due to sliding problem (see fig. 8).
Fig. 8: Relation between angular velocity and driving frequency
(b)After insertion of anti-gap lever reverse mechanism
Figure 7 shows the structure of anti-reverse mechanism. In fig. 7 (a), the anti-gap lever is still in the initial position, while in fig. 7 (b), the anti-gap lever is pushed into working position, i.e. locked gap was eliminated in Finally, the rotational electrostatic motor has been tested for performance. They were driven by = 80V) with different frequencies from 1Hz to 30Hz. When driving wer than 20Hz, the angular velocity of the ratchet ring was proportional with the frequency and matched very well with theoretical calculation. Beyond this range, the angular velocity was saturated due to sliding problem (see fig. 8).
PHỤ LỤC
NGUYỄN ĐÌNH HƯỚNG 77
4. CONCLUSIONS
This paper has presented the design, fabrication and testing of a silicon micro rotational motor. The motor is actuated by electrostatic comb drive actuator and ratchet mechanism. Novel design of anti-reverse mechanism overcomes the gap, which is inherently unavoidable during fabrication process. The motor worked well up to frequency of 20Hz. Beyond this value, the sliding problem was occurred. Improvement of the driving ratchet rack is going on and the result will be presented at the conference. Rotation movement of the micro motor can be improved and used in micro gearing systems for transmission and changing angular velocity, as well as in micro clock.
REFERENCES
[1] Tang W C, Nguyen T H and Howe R T 1989,
“Laterally Driven Polysilicon Resonant
Microstructures”, Tech. Dig. IEEE Micro
Electro Mech. Syst Workshop (1989), pp 53-59.
[2] Tang W C, Nguyen T H, Michael W J and Howe R T 1990, “Electrostatic-comb Drive of Lateral Polysilicon Resonators”, Sensors and Actuators
A21-A23 (1990), pp 328-331.
[3] Johnson W A and Warne L K 1995, “Electrophysics of Micromechanical Comb Actuators”, J. Microelectromech. Systems Vol.4, No.1, (1995), pp 49-59.
[4] Rob Legtenberg, A W Groeneveld and M Elwenspoek, “Comb-drive Actuators for Large Displacements”, J. Micromech. Microeng. 6
(1996) pp 320-329.
[5] J D Grade, H Jerman and T W Kenny, “Design of Large Deflection Electrostatic Actuators”,
Journal of MicroElectromech. Systems, Vol. 12,
No.3, (2001).
[6] T Y Harness and R A Richard, “Characteristic modes of Electrostatic Comb-Drive X-Y Microactuators”, J. Micromech. Microeng. 10
(2000), pp 7-14.
[7] E I Garcia and J J Sniegowski, “Surface Micromachined Microengine as the Driver for
Micromechanical Gears”, Transducers’95,
Stockholm, Sweden (1995), pp 365-368. [8] J J Sniegowski and E I Garcia, “Surface-
Micromachined Gear Trains Driven by an On- Chip Electrostatic Microengine”, IEEE Electron
Device Letters, Vol. 17, No. 7, (1996), pp 366-
368.
[9] R Yeh, S Hollar and Kristofer S J Pister, “Single Mask, Large Force, and Large Displacement Electrostatic Linear Inchworm Motors”, J. Microelectromech. Syst. (2002), Vol.11, pp 330-
336.
[10] S -C Kim and S H Kim, “Precise Rotary Motor by Inchworm Motion Using Dual Wrap Belt”,
Review of Scientific and Instrument, Vol. 70,
No. 5, (1999), pp 2546-2550.
[11] Firas N. Sammoura, “Novel Rotary Inchworm Motor”,robotics.eecs.berkeley.edu/~pister/245/p
roject/Sammoura.pdf
[12] Danelle M. Tanner et al, “Reliability of a MEMS Torsional Ratcheting Actuator”, IEEE - 39th Annual International Reliability Physics Symposium, Orlando, Florida, (2001), pp 81-90.
[13] E Sacks and S M Barnes, “Computer-Aided Kinematic Design of a Torsional Ratcheting Actuator”, Proc. of the Fourth International Conference on Modeling and Simulation of Microsystems, Hilton Head, SC, (2001).
[14] Phuc Hong Pham et al, “Straight Movement of
Micro Containers Based on Ratchet
Mechanism and Electrostatic Comb-Drive Actuators”, J. Micromech. Microeng. Vol.16,