Ctdmm Newsletter August 2008

Vol 1. No.1 October 2008

NEWSLETTER

By A. Marzuki Technical Consultant of C-RAD Technologies

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Highlights&News 1. IC ranking (Fabless) in the world: Qualcomm, Broadcom …, please see at this URL for more info. http://www.icinsights.com/news/bulletins/bulletins2008/bulletin2 0080801.html 2. Wireless Transfer Technology which was announced in 2006 by MIT is a fascinating research topic, http://www.mit.edu/~soljacic/wireless_power.html. Product based on this technology is currently being pursued. So hopefully we can see a product that recharge your battery’s hand phone wirelessly in the future! 3. Femtocell development is to configure each house as smaller version of ‘base station’, it is another version of Picocell. Femtocell is thought could improve the cost and efficiency of the network, it will be connected with broadband IP in house. It seems a lot of work need to be done to roll out this technology! 4. Lead-Free material is thought good to nature, is it so? Some say it causes in increase on Tin usage, and we back to square one, as Tin Mining is not good for nature. What do you think? 5. Wireless PAN at 60 GHz for high definition TV is thought to offer very high speed, high data rate wireless connectivity, but the frequency is one of the resonant frequencies of water. Unless we are shielded by metal, the frequency can be used at will, maybe at different frequency? But we don’t want to waste tremendous research effort on 60 GHz circuit design.

Please email your comments to [email protected]

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Circuit Techniques 1. Voltage reference circuit which is much smaller than standard band-gap circuit employs PTAT and CTAT current sources. Ref1: A voltage reference circuit for current source of RFIC block, http://www.emeraldinsight.com/10.1108/13565360810889593 Ref2: Low Power Bandgap Circuit, WIPO, WO 03/050847 A2

Please email your comments to [email protected]

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Articles

Si N MIM Capacitors Modeling for MMIC Applications 3 4 1 1 1 1 2 R. Sanusi , Mohd Azmi Ismail , Mohd. Nizam Othman , A.I. Abd. Rahim , A. Marzuki 1 1 Mohamed Razman Yahya and Abdul Fatah Awang Mat 1 TM Research & Development TMR&D Innovation Centre Lingkaran Teknokrat Timur 63000 Cyberjaya Selangor Darul Ehsan. 2 School of Electrical Engineering, Universiti Sains Malaysia (USM), 14300 Nibong Tebal, Pulau Pinang, Malaysia Email : [email protected]

Abstract Silicon nitride (Si N ) metal-insulator-metal (MIM) modelling at preliminary stage 3

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based on High Electron Mobility Transistor (HEMTS) on Gallium Arsenide (GaAs) substrates are presented. Device measurement and simulation of the Si3N4 MIM capacitor is performed in the frequency range of 2 to 50 GHz to generate S-parameters data. The behaviour of the capacitor as a function of the operating frequencies is studied. The equivalent circuit of Si3N4 MIM capacitor is proposed representing the behaviour of the devices. I. INTRODUCTION The Metal-Insulator-Metal (MIM) capacitor is a key passive component in MMIC’s technology for decoupling, filtering, oscillating, bypassing and matching functions [1] and is widely used in wireless 3G, WiMAX and Wi-Fi systems. MIM capacitors are desirable in MMICs applications because of its high capacitance density that increases circuit density and further reduces the fabrication cost and maximize the number of components per unit chip area. MIM capacitor provides good voltage linearity properties [2]. Overlay capacitors is used in MMIC applications like power and low noise amplifier. These overlay capacitor consist of a metal-insulator-metal (MIM capacitor), with the most common insulator being silicon nitride, Si N . Si N has fairly high relative permittivity (ε ), and can also 3

4

3

4

r

be used for passivating the exposed GaAs in the active devices. MIM capacitor can also be used to realise small value of capacitors for applications such as matching networks, and it is significantly small. MIM capacitor with air-bridge is basically one of MIM capacitor type. This paper presents a modelling simulation of Si N MIM capacitor performance up to 50 GHz. 3

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Two square dimensions of Si N MIM capacitor is discussed in the study, i.e 70 µm x 70 µm and 3

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100 µm x 100 µm. A new equivalent circuit representing the performance of Si3N4 MIM capacitor is proposed by including the metal and substrate parasitic effect.

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II. EXPERIMENT PROCEDURE Figure 1 shows the top view and the cross-section of Si N MIM capacitor. Top view shows the 3 4 bottom and top metal named metal 2 and metal 3 respectively, while the cross-section view illustrated the thickness of the metal and insulator for the device with Si3N4 as passivation of the device. It consist of 100 µm of GaAs substrate, 0.12 µm thickness of Si3N4 sandwiched between the metal 2 and metal 3 with thicknesses 0.4 µm and 3.12 µm respectively. The complete capacitor is covered by a layer of nitride with a thickness of 0.12 µm which passivate the whole structure. New equivalent circuit is proposed to show the performance of Si3N4 MIM capacitor, but this circuit is still in the beginning stage of the modeling process. Equivalent circuit of Si3N4 MIM capacitor is depicted in Figure 2. Cm2 represent the parasitic effect associated with the bottom metal or metal 2. C is the required value for the capacitor and Rloss is the parasitic loss that associated to C. C

m3

and R

m3

are the parasitic effect associated with the top metal or metal 3.

Finally, Csub and Rsub are the parasitic effect that associated with the substrate. Parasitic effect description is explained in Table 1.

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Device measurement was performed in S-parameter environment using in-house microprobe station. The measurement result was then imported into S2P component in ADS window to perform smith-chart plot and compared it with the proposed equivalent circuit model using the lumped elements through two port schematic simulation. Si N MIM capacitor measurement as 3

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depicted in Figure 3 is connected to RF pad.

Device C

m2

Table 1: Equivalent circuit description Description Capacitance between bottom metal (metal 2) and substrate

C R

Main value of capacitance Dielectric loss

C

Capacitance between bottom metal and substrate

loss

R C R

m3

m3

sub sub

Resistance between bottom metal and substrate Substrate capacitance Substrate resistance

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III. RESULT AND DISCUSSION

S-parameter simulation result for Si3N4 MIM capacitor 70 µm x 70 µm is shown in Figure 4, 5 and 6 below. S(1,1) is to obtain the value of the measured data and S(3,3) indicates the value of simulation using the proposed equivalent circuit model. In Figure 4, the data of S(3,3) is similar to S(1,1) from 2 GHz to 15 GHz, but it starts to disperse from S(1,1) at frequency near to 15 GHz up to 38 GHz, this situation is depicted in Figure 5. This happens due to the value of Rsub and Csub which are optimized. At frequency is between 45 GHz to 50 GHz, the measured Si3N4 MIM capacitor device resonates 2 times, and we can see that S(3,3) of the proposed equivalent circuit cannot be modelled S(1,1) precisely. Figure 6 shows that the Si3N4 MIM capacitor is working as a capacitor solely without

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having inductance behaviour. The capacitance value for 70 µm x 70 µm Si3N4 MIM capacitor is obtained through the imaginary admittance value as defined in ADS 2005 as explained from (1) to (3), and the values are 2.157 pF for the measured device and 2.3737 pF for the proposed equivalent circuit.

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Figure 7, 8 and 9 show the S-parameter simulation for 100 µm x 100 µm Si N MIM capacitor. 3 4 From the figures, the function of S(1,1) and S(3,3) are similar to 70 µm x 70 µm Si3N4 MIM capacitor. In Figure 7, S(3,3) of the proposed equivalent circuit model behaves similarly to the measured S(1,1) data. This means that the proposed equivalent circuit model performance is very good for larger device and higher frequency. Figure 8 shows the close up simulation of 100 µm x 100 µm Si3N4 MIM capacitor at frequencies above 15 GHz. From the figure, it is obtained that the device starts to resonate at 16.88 GHz. Figure 9 shows that Si3N4 MIM capacitor is working as a capacitor solely without having inductance effect. The capacitance values that are defined using the same technique stated in (1) to (3) are 4.372 pF for the measured device and 4.2905 pF for the proposed equivalent circuit.

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The proposed Si N MIM capacitor equivalent circuit model value using lumped elements is 3

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explained in Table 2. The prime capacitance value for 70 µm x 70 µm is 2.3737 pF and for 100 µm x 100 µm is 4.2905 pF. The proposed equivalent circuit model used for 70 µm x 70 µm does not perform very well at higher frequency than 15 GHz, hence the elements value of Rsub and Csub which give the effect for high frequency must be tuned and optimized accordingly. Table 2 Optimization results of Si N MIM capacitor equivalent circuit 3

Device C

4

70 µm x 70 µm

100 µm x 100 um

3 fF

0.001 fF

C R

2.3737 pF 0.472 Ω

4.2905 pF 4.547 Ω

C

0.1 fF

0.001 fF

4kΩ

91.876 Ω

4 fF

16.4218 fF

697 Ω

436 Ω

m2

loss

R C R

m3 m3

sub sub

IV. CONCLUSION S-parameter simulation of the proposed equivalent circuit model representing Si3N4 MIM capacitor performed very well at high and low frequency if compared to measure Si3N4 MIM capacitor device especially device with dimension 100 µm x 100 µm. Hence, some modification of equivalent circuit model for smaller dimension (< 70 µm x 70 µm) Si3N4 MIM capacitor will be performed in the near future.

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ACKNOWLEDGEMENT The author would like to thank TM R&D Sdn. Bhd. for providing the grant for this work under Project No: R05-0607-0. The help from Advanced RF systems Cluster is greatly appreciated for guidance in using ADS-Momentum Simulator. REFERENCES [1] M. Engels and R.H. Jansen, “Rigorous 3D EM Simulation and An Efficient Approximate Model of MMIC Overlay Capacitors with Multiple Feedpoints”, IEEE MTT-S International Microwave Symposium Digest, 14-18 Jun 1993, Page(s): 757-760 vol.2. [2] Piquet, J.; Cueto, O.; Charlet, F.; Thomas, M.; Bermond, C.; Farcy, A.; Torres, J.; Flechet, B, “Simulation and Characterization of High-frequency Performances of Advanced MIM Capacitors”, SolidState Device Research Conference, 12-16 Sept. 2005, Page(s):497 – 500 [3] Masa Asahara, “A Novel Approach to Modeling Metal-Insulator-Metal Capacitors Over Vias With Significant Electrical Length”, IEEE Transaction on Microwave Theory and techniques, Vol. 55, No. 4, April 2007, Page(s) : 709 – 714 [4] Liu Lintao, Wnag Jiniang, Feng-Chang Lai, “A New Equivalebt Circuit Model of MIM Capacitor for RFIC”, Microwave and Milimeter Wave Technology, pp. 1 – 3, April 2007. [5] Anders Mellberg, Jorgen Stenarson, “An Evaluation of Three Simple Scalable MIM Capacitor Models”, Microwave and Techniques, vol. 54, no. 1, pp. 169 – 172, January 2006 [6] Lombard, P.; Arnould, J.-D.; Exshaw, O.; Eusebe, H.; Benech, P.; Farcy, A.; Torres, J.; “MIM capacitors model determination and analysis of parameter influence”, IEEE International Symposium on Industrial Electronics, Vol 3, Page(s):1129 – 1132, June 2005

Rasidah Sanusi received her B. Eng. degree in Electrical and Electronic Engineering from University Putra Malaysia (UPM) in 2002. Upon graduation she worked as a Graduated Research Assistant (GRA) at UPM. She is currently pursuing her Masters degree in Electronics at the same university. In 2004, she joined Telekom Research & Development Sdn. Bhd. as an assistant researcher in the Microelectronis and Nano technology group. She is currently involved in the MMICs application design based on III-V material.

About CTDMM: A not for profit group with interest in Circuit Technique, Design Methodology and Modeling.Contact: [email protected] About CTDMM Newsletter: Newsletter which cover news and articles from industry and academia. The main purpose is to share knowledge and news within the Microelectronics players. Submit news or article to [email protected]. Authors to the articles are responsible to the articles and have the right to his/her article and work.

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