ES434 2021 Assignment 2: Design Briefing (set by V.A.Shah and J. W. Gardner) Page 1
ES434 2021: ASICS, MEMS and Smart Devices
Design, Layout & Simulation of a MEMS Capacitive Pressure Sensor
Assignment 2 (Design Report set by V.A. Shah and J. W. Gardner)
Submission Date: Monday, Week 17
Briefing
This assignment is worth 30% of the module credits (4.5 Credits) in the form of a word report
up to 2,000 words and software design files. The principle learning outcome is:
“Design ASICS and MEMS through practical experience using typical modern Computer Aided
Design software for this task”
You will design and simulate a MEMS device using the commercial ASIC and MEMS designing
software (Cadence virtuoso and Coventor MEMS+) and background information given in the
module textbook and lecture notes.
The word report (12 pt font; 1.5 line spacing) should be a comprehensive report on your
design methodology and results, including figures of the simulations. Please zip together the
computer software design files with your word report. The design files will be opened by the
marker to clarify a result or check for plagiarism. Please ensure all files and folder structures
are clear with no other unnecessary files. This should include a readme file with a description
of the folder tree.
Description of Assignment
In your assignment, you will design a capacitive pressure sensor using the 45 nm generic
design package. This sensor should measure ± 1 bar of pressure change with corresponding
drive and sensing circuitry
The output of the MEMS and ASIC will be an analogue signal that can be read by an Adafruit
Feather (Figure 1, Adafruit Feather 328P - Atmega328P 3.3V @ 8 MHz – technical datasheet
is provided). The MEMS chip should also be driven by the Atmega328P unit.

Figure 1: Adafruit feather 328P.
ES434 2021 Assignment 2: Design Briefing (set by V.A.Shah and J. W. Gardner) Page 2
Task 1 - Design Principle of Polysilicon MEMS Pressure Sensor
The MEMS pressure sensor is made from a polysilicon diaphragm that can detect ± 1 bar of
pressure change and its corresponding drive and sensing circuitry.
Pressure sensors are used in a range of industries and applications, such as automotive,
biomedical, aviation, etc. They have many different types and in this assignment, it is based
on capacitive measurements.
A basic capacitive pressure sensor, as shown in Figure 2, consists of:
1. A circular polysilicon diaphragm.
2. A silicon substrate with a capacitive plate.
3. A sealed cavity between the diaphragm and the plate that changes with pressure.
The nature of this pressure sensor is described in the module textbook, the lecture slides and
covered in seminar. (Note: Please familiarise yourself with this material.)

Sub-components
 Create a circular pressure sensor with above shown parts using Coventor MEMS+. Use the
processing steps in Figure 3 as an example.
 The dimensions of your design should correspond to preliminary capacitive calculations.
It is expected that your report will contain these calculations and evidence of simulation
and output response.
 This should accompany the explanation to device operation under analysis of variation in
pressures (±1 bar) and dimensional design variation.
 Consider if the layout should have a reference MOS capacitor.
 Additional marks will be given if different and suitable diaphragm materials can be
investigated and compared.
 In your report, you should be able to provide an explanation of your design with proofs
such as figures, results and calculations. Both the design and the report need to be
submitted and assessed before the deadline.

Figure 2: an example of actual pressure sensor and its modelled equivalent.
ES434 2021 Assignment 2: Design Briefing (set by V.A.Shah and J. W. Gardner) Page 3

Task 2 – Design of the ASIC
 Your ASIC should then take the sensor electrical model from MEMS+ then place it into
cadence virtuoso for further design and simulation of the drive and readout circuitry
for the sensor
 Consider if your design requires a drive source, amplification, buffer, timing and/or
filtering. Any of these components should be simulated in cadence virtuoso to
measure the maximum change of capacitance when experiencing ± 1 bar of pressure
change at room temperature.
 An example circuit provided in the seminar is shown in Figure 4 for capacitive readout.
(Note: the layout of an ADC is not needed as there is one provided by the Adafruit
microprocessor unit).
 Layout your circuit as an ASIC chip with schematic driven layout in cadence. Run
simulations to match the layout with schematic. Structure your components to
minimise the area size.
 In your report, you should be able to provide an explanation of your design with proofs
such as figures, results and calculations. Both the design and the report need to be
submitted and assessed before the deadline.

Figure 3: MEMS+ Processing Steps.
ES434 2021 Assignment 2: Design Briefing (set by V.A.Shah and J. W. Gardner) Page 4

Task 3 – Application specific packaging and costing of the ASIC and MEMS
 Estimate the cost of your MEMS and ASIC chips based upon a standard Europractice MPW
run. (Please use the ON Semi 0.35 μ C035 standard price list for mm2/euro given,
https://europractice-ic.com/prices-2021/).
 Please comment on the type of integration and packaging which you could incorporate
the ASIC and MEMS together. Try to estimate also the cost to mount, wire-bond and
mount in your chosen chip carrier.
 Estimate the power consumption of your MEMS ASIC chip and comment on this.
 Discuss the implementation of this MEMS chip in a real-world application and any issues
that could affect its performance and accuracy.



Figure 4: Possible sensing circuits to feed into the microcontroller ADC. (Yoo, Y.; Choi, B.-
D. Readout Circuits for Capacitive Sensors. Micromachines 2021, 12, 960 Y, Zhang, Journal of
Microelectromechanical Systems, vol. 27, no. 4, pp. 667-676, Aug. 2018.)

ES434 2021 Assignment 2: Design Briefing (set by V.A.Shah and J. W. Gardner) Page 5
Design Criteria & Marking Strategy
This is a semi-open ended design brief as you can decide the size of the MEMS sensor in
addition to the ASIC drive/sense circuitry that you want to use. In your answer, you are
expected to describe your design, give the preliminary design calculations, and simulations
performed to verify and correct the design so that its expected behaviour is compared to the
simulation.

Your reports will be marked in the following categories:
1. MEMS Pressure sensor design, simulations and discussion (MEMS+) (30%).
2. Circuit design, simulations and discussion of the ASIC chip (Virtuoso) (30%)
3. Combination design and simulations with layouts (20%)
4. Intellectual discussion/cost & power analysis/practical considerations (20%)





Dr Vishal Shah and Prof Julian Gardner
November 2021

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