On-Chip Hotplate for Temperature Control of Cmos Saw Resonators
📝 Abstract
Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents the design, modeling and characterization of integrated dual-serpentine polysilicon resistors as a method for temperature control of CMOS SAW resonators. The design employs the oven control temperature stabilization scheme where the device’s temperature is elevated to higher than Tmax to maintain constant device temperature. The efficiency of the polysilicon resistor as a heating element was verified through a 1-D partial differential equation model, 3-D CoventorWare finite element simulations and measurements using Compix thermal camera. To verify that the on-chip hotplate is effective as a temperature control method, both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of -97.2 ppm/deg C has been reduced to -23.19 ppm/deg C when heated to 56 deg C.
💡 Analysis
Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents the design, modeling and characterization of integrated dual-serpentine polysilicon resistors as a method for temperature control of CMOS SAW resonators. The design employs the oven control temperature stabilization scheme where the device’s temperature is elevated to higher than Tmax to maintain constant device temperature. The efficiency of the polysilicon resistor as a heating element was verified through a 1-D partial differential equation model, 3-D CoventorWare finite element simulations and measurements using Compix thermal camera. To verify that the on-chip hotplate is effective as a temperature control method, both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of -97.2 ppm/deg C has been reduced to -23.19 ppm/deg C when heated to 56 deg C.
📄 Content
9-11 April 2008
Substrate
Ground
Shield
Reflector
Reflector
Input
IDT
Output
IDT
SiO
Fig.1. Implementation of a two-port SAW resonator
structure in CMOS. For clarity, the piezoelectric ZnO
layer is not shown [1],
SiO2
ZnO Metal 1
Si Substrate
Polysilicon Transducer Fig. 2. Cross-section of CMOS SAW Resonator with embedded heaters On-Chip Hotplate for Temperature Control of CMOS SAW Resonators
A. N. Nordin1, I. Voiculescu2 and M. Zaghloul1 1 Department of Electrical and Computer Engineering, George Washington University, Washington DC, USA 2Department of Mechanical Engineering, City College of New York, New York, USA
Abstract-Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents the design, modeling and characterization of integrated dual-serpentine polysilicon resistors as a method of temperature control for CMOS SAW resonators. The design employs the oven control temperature stabilization scheme where the device’s temperature is elevated to higher than Tmax to maintain constant device temperature. The efficiency of the polysilicon resistor as a heating element was verified through a 1-D partial differential equation model, 3-D CoventorWare® finite element simulations and measurements using Compix® thermal camera. To verify that the on-chip hotplate is effective as a temperature control method, both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of -97.2 ppm/oC has been reduced to -23.19 ppm/oC when heated to 56oC.
I. INTRODUCTION The common usage of SAW resonators with RF integrated circuits (IC) has motivated its fabrication using standard IC fabrication processes. Fully integrated CMOS SAW resonators with frequencies ranging from 500 MHz to 1 GHz have been successfully fabricated [1]. For device stability, a small variation of frequency with temperature (less than 1ppm/oC) is often desired. SAW devices employing ZnO as its piezoelectric material have been reported to have negative temperature coefficient frequency (TCF) [2, 3]. Various methods have been employed to reduce the effect of the negative (TCF) for resonators utilizing ZnO such as adding control-circuitry [4], using quartz substrates [2], and layering positive TCF SiO2 layers [3]. For our device, we have proposed a simple solution of an embedded heater so that additional temperature compensation circuitry and alteration of the device structure or layers would not be required. Temperature compensation is achieved by heating the resonator structure to a temperature above its typical operating temperature causing the device to be independent of the ambient temperature.
II. DEVICE STRUCTURE AND FABRICATION Fig. 1 shows the structure of a two-port CMOS SAW resonator that consists of input and output interdigital transducers (IDTs), with a bank of shorted reflectors on each side. When a sinusoidal signal is injected at the input port, acoustic waves propagate in the piezoelectric layer above the IDTs in both directions. The acoustic wave is detected and translated back into an electrical signal at the output port. The reflectors minimize losses by containing the acoustic waves within the cavity, creating standing waves. The device’s resonant frequency is determined by the periodic distance (λ) of the IDT. The IDTs, reflectors and ground shield were implemented using standard CMOS layers [1]. To incorporate a heating element for the CMOS SAW resonator, it is advantageous to utilize material layers inherent in CMOS IC technology. Polysilicon with sheet resistivity of 22.8 Ω/sq. [5], is commonly used as a heating ©EDA Publishing/DTIP 2008 ISBN: 978-2-35500-006-5
Fig. 4. Steady-state temperature distribution of polysilicon heater with 1 V applied input. t L w -x +x y 0 Tamb Tamb Heater (b) Fig. 3. (a) Heater geometry and dimensions. (b) Simple model for 1-D heat flow Resistor 1 Resistor 2 TABLE 7-1: POLYSILICON HEATER DIMENSIONS AND 1-D STEADY STATE TEMPERATURE
L (µm) W (µm) T (µm) R (kΩ) Applied Voltage (V) Temp (K) R1 4088 12 0.3 5.05 1 708.82 R2 3993 12 0.3 4.99 1 699.33 (a) element for CMOS MEMS devices. The choice of polysilicon as the heater layer for our device is ideal since it does not disturb the present device layers. An added advantage is that the ground shield layer now not only provides isolation of the resonator from electromagnetic feedthrough but also acts as an even temperature distributor. This resonator with temperature control elements was fabricated using AMI C5 0.6 µm CMOS process. A series of IC compatible post-processing steps were implemented to integrate the piezoelectric ZnO layer on top of
This content is AI-processed based on ArXiv data.