tailieunhanh - Advanced Microwave Circuits and Systems P12

Nhiều chương trình CAD hiện nay cho phép tạo ra các mô hình ba chiều để có thể nhìn từ mọi góc độ. Các chương trình CAD mô hình hóa vật thể đặc tiên tiến là một hệ thống thiết kế hiện thực ảo. Những mô hình đặc như vậy có thể được dùng làm cơ sở cho các phân tích phần tử hữu hạn (FEA) và / hoặc tính toán động lực dòng chảy (CFD) của thiết kế. Cho đến ứng dụng gia công với trợ giúp máy tính (CAM), những mô hình này cũng có thể được dùng. | 324 Advanced Microwave Circuits and Systems simulation in order to obtain the same pull-in pull-out characteristic. A residual air gap of 590 nm is set in the simulation when the plate collapses onto the substrate. Such value comes from the extracted Cmax discussed in previous subsection. Fig. 10 reports the measured and simulated pull-in pull-out characteristic of the RF-MEMS varactor showing a very good agreement of the two curves. In particular the measured pull-in voltage 15 V and pull-out voltage 9 V are predicted very accurately by the compact models in Spectre. The characteristics of Fig. 10 show the typical hysteresis of MEMS devices. Applied bias Volts Fig. 10. Measured static pull-in pull-out characteristic compared to the one simulated with the schematic of Fig. 9-top within Cadence DC simulation in Spectre . Arrows help in identifying the pull-in pull-out hysteresis. More in details the good agreement of the measured and simulated pull-in voltage confirms both that the elastic constant k is modelled correctly in the Spectre simulation and that the initial air gap g is properly set Iannacci 2007 . After this consideration the good superposition of the measured and simulated pull-out voltage Vpo finally confirms that the residual air gap tair previously extracted from RF measurement is correct since the Vpo depends on it as follows Iannacci et al. 2009 b K PO 2kg t D t 8 t8ir ox air 5 where tair is the oxide layer thickness A the electrodes area ox and air the dielectric constant of the oxide and air respectively. A further confirmation of the DUT non-idealities comes from the observation of Fig. 10. Starting from the pull-in voltage 15 V and rising up to 20 V the vertical quote of the switch is not constant as it would be expected but tends to decrease of about 200 nm. Interpretation of such an awkward behaviour is straightforward by knowing that the profiling system determines each point of the pull-in pull-out characteristic as the mean value of all .