Kanti Prasad

Bandwidth Improvement Methods In Acoustically-Coupled Thin Film BAW Devices

In this paper, the results of a stacked crystal filter (SCF) are presented. It is shown that the bandwidth of the SCF can be designed by choice of electrode materials, device dimensions and use of external components such as inductors. This paper also discusses the fabrication of SCF along with the device layouts. A single stage and a two-stage SCF are designed and it is shown that the bandwidth of two-stage can only be increased if the inductor is connected between stages

Temperature dependent linear HEMT model extracted with multi-temperature optimization

Temperature dependent model is conventionally developed with 1) individual linear model extraction at each temperature and 2) temperature dependence extraction for each model parameter. A novel approach based on a multi-temperature optimization is proposed in this study. The new approach is faster and more accurate since the linear models at different temperatures are extracted simultaneously and inter-relatedly. It has been found, based on the model extracted, that there is a specific gate-source voltage of Vgs0, where the transconductance (Gm) keeps constant versus temperature. Gm increases (decreases) with temperature for Vgs<;Vgs0 (Vgs>;Vgs0). With increasing temperature, a substantial decrease in extrinsic inductance is also observed. Our findings are believed to be useful for designing HEMT amplifiers with less temperature dependence.

Inertial MEMS Test Challenges

This paper describes the challenges in Inertial Micro-Electro Mechanical System (MEMS) testing as compared to standard Application Specific Integrated Circuit (ASIC) testing. The most significant challenge in MEMS testing is having moving silicon parts surrounded by integrated circuitry (IC). Testing integrated circuits, whether analog or digital has its own complexity. However MEMS testing need to be more refined and accurate due to their criticality in applications like automobile airbag trigger, activate skid control, health care, etc. In addition to electrical testing MEMS also requires mechanical testing (Sensitivity) which is an important test parameter to characterize the device and market it with guarantee.

Comparing process flow of monolithic CMOS-MEMS intergration on SOI wafers with monolithic BiMOS-MEMS integration on Silicon wafer

This paper describes the two different integrated fabrication process flows for microelectromechanical systems (MEMS) accelerometer with surface micromachining technology at Analog Devices (ADI). Each method has its own identity with several advantages and disadvantages with respect to each other. CMOS-MEMS are fabricated using silicon-on-insulator (SOI) substrate, which allows the monolithic integration of the mechanical transducer and the control electronics on the device single crystal silicon layer. However, BiMOS-MEMS are fabricated on silicon substrates for building the control electronics and where thick poly-silicon is added to form the mechanical sensor. The integrated circuit (IC) industry evolution in two decades has made great strides and provided a mature infrastructure for surface micromachining by which successful miniaturization and multiplicity of traditional electronics systems have been applied to MEMS devices. . We report the fabrication flow for the two integrated MEMS processes incorporating MEMS with the control electronics and how they compare.

Modeling of RF- MEMS BAW Resonator

Due to the demand of smaller and more portable devices the applications of MEMS resonators are rapidly increasing. Solidly Mounted Resonators (SMR) based on Bulk Acoustic Wave (BAW) technology follow MEMS principles to build high performance microwave filters for RF communication. In this paper we will provide the architecture of SMRs by discussing the designing aspects of its core structures which are within foundry CMOS processes using RF design software Advanced Design System (ADS). Conventional VLSI processes are followed for the fabrication of the SMRs. The results from the fabricated data are compared and discussed.

RF-MEMS resonator design for parameter characterization

A unique methodology involving Bulk Acoustic Wave (BAW) Solidly Mounted Resonators (SMRs) is presented in this paper which can be used to extract precise materials information that is vital to designing high performance RF filters. The novel approach allows simultaneous extraction of multiple parameters for multiple materials. Changes in materials properties over temperature can also be extracted.

Multi-device Optimization for Scalable DC HEMT Model with Self-Heating Effect

This paper presents a new approach for extracting a scalable DC HEMT model. Scaling rules with unknown coefficients are assumed for each size dependent parameter, and the model parameter of different devices is thus correlated. A scalable model can then be extracted by multi-device optimization. The optimization is carried out on five devices with different gate width. In this way, accurate scaling rules for each parameter and very good I-V fittings for each device have been achieved simultaneously.

Spurious modes suppression in Stacked Crystal Filter

Stacked Crystal Filters (SCFs) are used in Bandpass filters and other applications where frequency control is required. SCFs use the Solidly Mounted Resonator (SMR) structure to enable operations at RF frequencies, typically 1–5 GHz. In the response spectrum of the SCFs, besides the main resonance mode, there are some unwanted additional modes present which affect the filters performance away from the primary passband frequency. A single passband is typically a required specification of a band pass filter; therefore the other unwanted modes are to be suppressed as a transmission band can manifest at each unwanted mode. It will turn out that with proper choice of layer materials and thicknesses the unwanted modes can be suppressed, but the level of suppression will be sensitive to the exact layer thicknesses fabricated. A research work is needed to focus on evaluating the materials used in the SCFs resonating mirror and seek a novel mirror methodology for the suppression of these unwanted modes even over manufacturing variations. In this paper, we will investigate careful control of the acoustic mirror stack above which the SMR stack is fabricated to create the SCF. By choosing appropriate materials and adjusting their respective thicknesses, the spurious modes can be suppressed without degrading the overall primary mode performance of the SCF. Trade-offs between the acoustic mirror properties relating to the filters addressable bandwidth, and the desired suppression of lateral modes of one/two stage SCFs will be discussed.

Feature Size and Density Effects in Wet Selective Etching of GaAs/AlAs p-HEMT Structures with Organic Acid - Peroxide Solutions.

Pseudomorphic HEMT (p-HEMT) devices are used in a number of wireless communication applications including power amplifiers in the 17–50 GHz range, low noise amplifiers and switches. Selective wet etching is often used to form the gate regions of these devices to avoid plasma damage associated with dry etching. We have investigated the wet etching of small (8μm to 0.5μm) features with organic acid - hydrogen peroxide solutions. Two acid solutions were used as a selective etchant for GaAs using AlAs etch stop layers in a p-HEMT structure grown by MBE. The etched features were characterized by AFM, SEM, and TEM techniques. The etch depth uniformity and reproducibility were found to depend on a number of factors including feature size, feature density, etching chemistry, agitation and surface tension. When features with a range of size and density were placed in close proximity in a layout we found that the etch rate of the different features was a function of density, size and most importantly the etch chemistry. One etchant solution exhibited a 12% difference in etch rate from the smallest feature to the largest, while another solution exhibited uniform etching of all features regardless of size or density. Both solutions produced specular etched surfaces in GaAs and AlGaAs. However, the AlAs etch stop showed a non-uniform surface morphology after etching. The surface morphology of the AlAs etch stop is one factor that limits the over etch which can be designed into the process. The most important factors to be considered in designing a selective etch process will be presented.

Partnership Between Education and Industry for Preparing Students for State-of-the-Art Vlsi Technology

Teaching students VLSI Design & Fabrication Technology is one of the most broadbased and costly endeavor. Regional industrial support has made it possible at University of Massachusetts Lowell. Educational instructions are not geared only towards teaching the fundamentals, but also to train the students with latest technological tools. cooperative industrial endeavors of the UMASS Lowell have resulted into a better VLSI program in general and improved design and fabrication methodologies in particular. This State-of-theArt technology is being upgraded continuously by the author and disseminated in the class room, reflecting latest upgrades. Owing to generous industrial support, the VLSI Technological challenge has certainly been accepted by UMASS Lowell. The